crypto: testmgr - change `guard` to unsigned char

When char is signed, storing the values 0xba (186) and 0xad (173) in the
`guard` array produces signed overflow. Change the type of `guard` to
static unsigned char to correct undefined behavior and reduce function
stack usage.

Signed-off-by: Joey Pabalinas <joeypabalinas@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/testmgr.c

@@ -185,7 +185,7 @@ static int ahash_partial_update(struct ahash_request **preq,
 	char *state;
 	struct ahash_request *req;
 	int statesize, ret = -EINVAL;
-	const char guard[] = { 0x00, 0xba, 0xad, 0x00 };
+	static const unsigned char guard[] = { 0x00, 0xba, 0xad, 0x00 };
 
 	req = *preq;
 	statesize = crypto_ahash_statesize(