Linux: Align MODULE_LICENSE macro text

Specify the lua and zstd license text in the manor in which the
kernel MODULE_LICENSE macro requires it.  The now duplicate entries
were merged and a comment added to make it clear what they apply to.

Reviewed-by: Christian Schwarz <christian.schwarz@nutanix.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes openzfs#13641

module/os/linux/zfs/zfs_ioctl_os.c

@@ -369,8 +369,7 @@ MODULE_ALIAS("zcommon");
 MODULE_ALIAS("zzstd");
 MODULE_DESCRIPTION("ZFS");
 MODULE_AUTHOR(ZFS_META_AUTHOR);
-MODULE_LICENSE("Lua: MIT");
-MODULE_LICENSE("zstd: Dual BSD/GPL");
-MODULE_LICENSE("Dual BSD/GPL");
+MODULE_LICENSE("Dual MIT/GPL"); /* lua */
+MODULE_LICENSE("Dual BSD/GPL"); /* zstd / misc */
 MODULE_LICENSE(ZFS_META_LICENSE);
 MODULE_VERSION(ZFS_META_VERSION "-" ZFS_META_RELEASE);