Update stdlib_bitsets.f90

For bitset_64 changed

integer(block_kind), private, allocatable :: block

to

integer(block_kind), private :: block = 0

Author: wclodius2

src/stdlib_bitsets.f90

@@ -1205,7 +1205,7 @@ end subroutine log64_assign_large
 !!
 !! Type for bitsets with no more than 64 bits.
         private
-        integer(block_kind), private, allocatable :: block
+        integer(block_kind), private :: block = 0
 
     contains