avcodec/hevc: fix chroma transform_add size

Fixes accessing misaligned address
Fixes: signal_sigsegv_1feb99c_10_signal_sigsegv_2d1d35c_79_cov_691940146_EXT_A_ericsson_3.bit

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/hevc.c

@@ -981,7 +981,7 @@ static int hls_transform_unit(HEVCContext *s, int x0, int y0,
                         for (i = 0; i < (size * size); i++) {
                             coeffs[i] = ((lc->tu.res_scale_val * coeffs_y[i]) >> 3);
                         }
-                        s->hevcdsp.transform_add[log2_trafo_size-2](dst, coeffs, stride);
+                        s->hevcdsp.transform_add[log2_trafo_size_c-2](dst, coeffs, stride);
                     }
             }
 
@@ -1010,7 +1010,7 @@ static int hls_transform_unit(HEVCContext *s, int x0, int y0,
                         for (i = 0; i < (size * size); i++) {
                             coeffs[i] = ((lc->tu.res_scale_val * coeffs_y[i]) >> 3);
                         }
-                        s->hevcdsp.transform_add[log2_trafo_size-2](dst, coeffs, stride);
+                        s->hevcdsp.transform_add[log2_trafo_size_c-2](dst, coeffs, stride);
                     }
             }
         } else if (blk_idx == 3) {