get_bits: remove unused assignment

Bug-Id: CID 1238816

libavcodec/get_bits.h

@@ -380,7 +380,7 @@ static inline int init_get_bits(GetBitContext *s, const uint8_t *buffer,
     int ret = 0;
 
     if (bit_size > INT_MAX - 7 || bit_size < 0 || !buffer) {
-        buffer_size = bit_size = 0;
+        bit_size    = 0;
         buffer      = NULL;
         ret         = AVERROR_INVALIDDATA;
     }