community/isa-l: fix build with gcc 14 on ppc64le
Fix -Wreturn-mismatch error on ppc64le, found on the 3.21 ppc64le builder (error log).
erasure_code/ppc64le/gf_vect_mul_vsx.c: In function '_gf_vect_mul_base':
erasure_code/ppc64le/gf_vect_mul_vsx.c:14:16: error: 'return' with a
value, in function returning void [-Wreturn-mismatch]
14 | return 0;
| ^
erasure_code/ppc64le/gf_vect_mul_vsx.c:6:13: note: declared here
6 | static void _gf_vect_mul_base(int len, unsigned char *a, unsigned char *src,
| ^~~~~~~~~~~~~~~~~