Handle current UBSAN errors on Fedora 39 and Fedora 40

[mcmilk]

Motivation and Context

The fixed size array sa_lengths[1] is used dynamicly and UBSAN warns about it:

[ 1110.124477] ------------[ cut here ]------------
[ 1110.126140] UBSAN: array-index-out-of-bounds in .../sa.c:766:21
[ 1110.130745] index 1 is out of range for type 'uint16_t [1]'

[ 1110.406282] UBSAN: array-index-out-of-bounds in .../sa.c:1934:29
[ 1110.411905] index 1 is out of range for type 'uint16_t [1]'

[ 1110.817251] UBSAN: array-index-out-of-bounds in .../sa.c:1734:24
[ 1110.821635] index 1 is out of range for type 'uint16_t [1]'

Description

Fix the header file and make sa_lengths variable: sa_lengths[1] -> sa_lengths[]

How Has This Been Tested?

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[mcmilk]

Test run with fix: https://github.com/mcmilk/zfs/actions/runs/10036702203
Test run without fix: https://github.com/mcmilk/zfs/actions/runs/10028261932

You see the UBSAN errors within the vm2: serial console output on Fedora 39 and Fedora 40.

[tonyhutter]

I'd like to go with the workaround in #16380, only because sizeof(sa_hdr_phys_t) would change with this PR, and I'm paranoid that that might break something like:

static int                                                                       
sa_find_sizes(sa_os_t *sa, sa_bulk_attr_t *attr_desc, int attr_count,            
    dmu_buf_t *db, sa_buf_type_t buftype, int full_space, int *index,            
    int *total, boolean_t *will_spill)   
{
...
       hdrsize = (SA_BONUSTYPE_FROM_DB(db) == DMU_OT_ZNODE) ? 0 :                
           sizeof (sa_hdr_phys_t); 

[mcmilk]

Obsoleted by #16380