prores: use natural integer type for the codebook index

The operations that use it require it to be promoted to a larger (natural)
type and thus perform sign extension on it.

While an optimal compiler may account for this, gcc 4.6 (for x86 Windows)
fails. Using the natural integer type provides a 2% speedup for Win64
and 1% for Win32.
Signed-off-by: NDiego Biurrun <diego@biurrun.de>

libavcodec/proresdec.c

@@ -289,7 +289,7 @@ static int decode_picture_header(ProresContext *ctx, const uint8_t *buf,
 /**
  * Read an unsigned rice/exp golomb codeword.
  */
-static inline int decode_vlc_codeword(GetBitContext *gb, uint8_t codebook)
+static inline int decode_vlc_codeword(GetBitContext *gb, unsigned codebook)
 {
     unsigned int rice_order, exp_order, switch_bits;
     unsigned int buf, code;

libavcodec/proresenc.c

@@ -229,7 +229,7 @@ static void get_slice_data(ProresContext *ctx, const uint16_t *src,
 /**
  * Write an unsigned rice/exp golomb codeword.
  */
-static inline void encode_vlc_codeword(PutBitContext *pb, uint8_t codebook, int val)
+static inline void encode_vlc_codeword(PutBitContext *pb, unsigned codebook, int val)
 {
     unsigned int rice_order, exp_order, switch_bits, switch_val;
     int exponent;
@@ -393,7 +393,7 @@ static int encode_slice(AVCodecContext *avctx, const AVFrame *pic,
     return total_size;
 }
 
-static inline int estimate_vlc(uint8_t codebook, int val)
+static inline int estimate_vlc(unsigned codebook, int val)
 {
     unsigned int rice_order, exp_order, switch_bits, switch_val;
     int exponent;