srtp: Mark a few variables as uninitialized

This squelches false positive warnings (with gcc) about them being
used uninitalized.

Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/srtp.c

@@ -121,8 +121,8 @@ int ff_srtp_decrypt(struct SRTPContext *s, uint8_t *buf, int *lenptr)
 {
     uint8_t iv[16] = { 0 }, hmac[20];
     int len = *lenptr;
-    int ext, seq_largest;
+    int ext, av_uninit(seq_largest);
-    uint32_t ssrc, roc;
+    uint32_t ssrc, av_uninit(roc);
     uint64_t index;
     int rtcp;