Vboot Reference: Add the "real" reference firmware verification function (VerifyFirmware).

src/platform/vboot_reference/crypto/sha_utility.c

Index: src/platform/vboot_reference/crypto/sha_utility.c
diff --git a/src/platform/vboot_reference/crypto/sha_utility.c b/src/platform/vboot_reference/crypto/sha_utility.c
index 5e3f7e07c4b663b6148f9ec0be29aa68747db4c7..e4c5e370510ad0b8002f9c824c1d852e275d3acf 100644
--- a/src/platform/vboot_reference/crypto/sha_utility.c
+++ b/src/platform/vboot_reference/crypto/sha_utility.c
@@ -108,7 +108,7 @@ uint8_t* DigestFile(char* input_file, int sig_algorithm) {
   return digest;
 }
 
-uint8_t* DigestBuf(uint8_t* buf, int len, int sig_algorithm) {
+uint8_t* DigestBuf(const uint8_t* buf, int len, int sig_algorithm) {
   uint8_t* digest = (uint8_t*) Malloc(SHA512_DIGEST_SIZE); /* Use the max. */
   /* Define an array mapping [sig_algorithm] to function pointers to the
    * SHA{1|256|512} functions.