amrwbdec: Decode the fr_quality bit properly

The way this bit is decoded was accidentally flipped in b70feb40,
leading to warnings "Encountered a bad or corrupted frame" for each
decoded frame.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/amrwbdec.c

@@ -122,7 +122,7 @@ static int decode_mime_header(AMRWBContext *ctx, const uint8_t *buf)
 {
     /* Decode frame header (1st octet) */
     ctx->fr_cur_mode  = buf[0] >> 3 & 0x0F;
-    ctx->fr_quality   = (buf[0] & 0x4) != 0x4;
+    ctx->fr_quality   = (buf[0] & 0x4) == 0x4;
 
     return 1;
 }