Silence a GCC false positive warning.

GCC 11.2.1 reportedly warns that CTR_DRBG_init may be passed an
uninitialized personalization buffer. This appears to be a false
positive, because personalization_len will be zero. But it's easy enough
to zero-initialize it, so silence the warning.

Bug: 432
Change-Id: I20f6b74e09f19962e8cae37d45090ff3d1c0215d
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/49245
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>

crypto/fipsmodule/rand/rand.c

@@ -356,7 +356,7 @@ void RAND_bytes_with_additional_data(uint8_t *out, size_t out_len,
     int used_cpu;
     rand_get_seed(state, seed, &used_cpu);
 
-    uint8_t personalization[CTR_DRBG_ENTROPY_LEN];
+    uint8_t personalization[CTR_DRBG_ENTROPY_LEN] = {0};
     size_t personalization_len = 0;
 #if defined(OPENSSL_URANDOM)
     // If we used RDRAND, also opportunistically read from the system. This