avutil/hmac: silence pointer type warnings

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/hmac.c

@@ -53,17 +53,17 @@ AVHMAC *av_hmac_alloc(enum AVHMACType type)
     case AV_HMAC_MD5:
         c->blocklen = 64;
         c->hashlen  = 16;
-        c->init     = av_md5_init;
-        c->update   = av_md5_update;
-        c->final    = av_md5_final;
+        c->init     = (void*)av_md5_init;
+        c->update   = (void*)av_md5_update;
+        c->final    = (void*)av_md5_final;
         c->hash     = av_md5_alloc();
         break;
     case AV_HMAC_SHA1:
         c->blocklen = 64;
         c->hashlen  = 20;
         c->init     = sha1_init;
-        c->update   = av_sha_update;
-        c->final    = av_sha_final;
+        c->update   = (void*)av_sha_update;
+        c->final    = (void*)av_sha_final;
         c->hash     = av_sha_alloc();
         break;
     default: