snowenc: mark some encode_subband arguments const.

This makes it more obvious that this function only does bitstream
encoding.
Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>

libavcodec/snowenc.c

@@ -827,7 +827,7 @@ static int get_4block_rd(SnowContext *s, int mb_x, int mb_y, int plane_index){
     return distortion + rate*penalty_factor;
 }
 
-static int encode_subband_c0run(SnowContext *s, SubBand *b, IDWTELEM *src, IDWTELEM *parent, int stride, int orientation){
+static int encode_subband_c0run(SnowContext *s, SubBand *b, const IDWTELEM *src, const IDWTELEM *parent, int stride, int orientation){
     const int w= b->width;
     const int h= b->height;
     int x, y;
@@ -947,7 +947,7 @@ static int encode_subband_c0run(SnowContext *s, SubBand *b, IDWTELEM *src, IDWTE
     return 0;
 }
 
-static int encode_subband(SnowContext *s, SubBand *b, IDWTELEM *src, IDWTELEM *parent, int stride, int orientation){
+static int encode_subband(SnowContext *s, SubBand *b, const IDWTELEM *src, const IDWTELEM *parent, int stride, int orientation){
 //    encode_subband_qtree(s, b, src, parent, stride, orientation);
 //    encode_subband_z0run(s, b, src, parent, stride, orientation);
     return encode_subband_c0run(s, b, src, parent, stride, orientation);