Use a pointer to module_hash in boringssl_fips_self_test() args.

1) Matches signature in internal.h
2) Works around presubmit build errors in Trusty: b/141974065

Nit: Should probably be const uint8_t *const module_hash
Change-Id: Id16ceea8442f4e8e588f84a8ef45e2320435809b
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/37904
Commit-Queue: Pete Bentley <prb@google.com>
Reviewed-by: Adam Langley <agl@google.com>

crypto/fipsmodule/self_check/self_check.c

diff --git a/crypto/fipsmodule/self_check/self_check.c b/crypto/fipsmodule/self_check/self_check.c
index 8a9e16b..d8a61c3 100644
--- a/crypto/fipsmodule/self_check/self_check.c
+++ b/crypto/fipsmodule/self_check/self_check.c
@@ -250,7 +250,7 @@
 #endif
 
 int boringssl_fips_self_test(
-    const uint8_t module_hash[kModuleDigestSize], size_t module_hash_len) {
+    const uint8_t *module_hash, size_t module_hash_len) {
 #if defined(BORINGSSL_FIPS_SELF_TEST_FLAG_FILE)
   char flag_path[sizeof(kFlagPrefix) + 2*kModuleDigestSize];
   if (module_hash_len != 0) {