Fix build of grfmt_jpeg2000.cpp

libjasper has recently changed `jas_matrix_get` from a macro to an inline function
(389951d071 in https://github.com/jasper-software/jasper), causing the build to fail.

Author: Windfisch

modules/imgcodecs/src/grfmt_jpeg2000.cpp

@@ -377,7 +377,7 @@ bool  Jpeg2KDecoder::readComponent8u( uchar *data, void *_buffer,
 
     for( y = 0; y < yend - ystart; )
     {
-        jas_seqent_t* pix_row = &jas_matrix_get( buffer, y / ystep, 0 );
+        jas_seqent_t* pix_row = jas_matrix_getref( buffer, y / ystep, 0 );
         uchar* dst = data + (y - yoffset) * step - xoffset;
 
         if( xstep == 1 )
@@ -443,7 +443,7 @@ bool  Jpeg2KDecoder::readComponent16u( unsigned short *data, void *_buffer,
 
     for( y = 0; y < yend - ystart; )
     {
-        jas_seqent_t* pix_row = &jas_matrix_get( buffer, y / ystep, 0 );
+        jas_seqent_t* pix_row = jas_matrix_getref( buffer, y / ystep, 0 );
         ushort* dst = data + (y - yoffset) * step - xoffset;
 
         if( xstep == 1 )