drm/amd/display: remove set but not used variable 'pixel_width'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/gpu/drm/amd/display/dc/dcn10/dcn10_dpp.c:137:11: warning: variable ‘pixel_width’ set but not used [-Wunused-but-set-variable]

It is introduced by commit 70ccab60 ("drm/amdgpu/display:
Add core dc support for DCN"), but never used, so remove it.
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zheng Bin <zhengbin13@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn10/dcn10_dpp.c

@@ -134,13 +134,6 @@ bool dpp1_get_optimal_number_of_taps(
 		struct scaler_data *scl_data,
 		const struct scaling_taps *in_taps)
 {
-	uint32_t pixel_width;
-
-	if (scl_data->viewport.width > scl_data->recout.width)
-		pixel_width = scl_data->recout.width;
-	else
-		pixel_width = scl_data->viewport.width;
-
 	/* Some ASICs does not support  FP16 scaling, so we reject modes require this*/
 	if (scl_data->format == PIXEL_FORMAT_FP16 &&
 		dpp->caps->dscl_data_proc_format == DSCL_DATA_PRCESSING_FIXED_FORMAT &&