selftests/bpf: fix test_loader check message

Seeing:

  process_subtest:PASS:Can't alloc specs array 0 nsec

... in verbose successful test log is very confusing. Use smaller
identifier-like test tag to denote that we are asserting specs array
allocation success.

Now it's much less distracting:

  process_subtest:PASS:specs_alloc 0 nsec
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20240105000909.2818934-2-andrii@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/test_loader.c

@@ -688,7 +688,7 @@ static void process_subtest(struct test_loader *tester,
 		++nr_progs;
 
 	specs = calloc(nr_progs, sizeof(struct test_spec));
-	if (!ASSERT_OK_PTR(specs, "Can't alloc specs array"))
+	if (!ASSERT_OK_PTR(specs, "specs_alloc"))
 		return;
 
 	i = 0;