perf bpf: Fix up build failure due to change of btf_vlen() return type

perf bpf: Fix up build failure due to change of btf_vlen() return type

Fix:

util/btf.c: In function '__btf_type__find_member_by_name':
util/btf.c:19:43: error: comparison of integer expressions of different signedness: 'int' and '__u32' {aka 'unsigned int'} [-Werror=sign-compare]
   19 |         for (i = 0, m = btf_members(t); i < btf_vlen(t); i++, m++) {
      |                                           ^

builtin-trace.c: In function 'syscall_arg__strtoul_btf_enum':
builtin-trace.c:967:27: error: comparison of integer expressions of different signedness: 'int' and '__u32' {aka 'unsigned int'} [-Werror=sign-compare]
  967 |         for (int i = 0; i < btf_vlen(bt); ++i, ++be) {
      |                           ^

by making the variable the same type as the function.

Committer note:

Add an extra hunk from Alan Maguire, fixing btf_enum_scnprintf().

Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>