drm/imx: Fix three kernel-doc warnings in dcss-scaler.c

drm/imx: Fix three kernel-doc warnings in dcss-scaler.c

Fix the following W=1 kerneldoc warnings by adding the missing parameter
descriptions for @phase0_identity and @nn_interpolation in
dcss_scaler_filter_design() and @phase0_identity in
dcss_scaler_gaussian_filter()

Warning: drivers/gpu/drm/imx/dcss/dcss-scaler.c:173 function parameter 'phase0_identity' not described in 'dcss_scaler_gaussian_filter'
Warning: drivers/gpu/drm/imx/dcss/dcss-scaler.c:270 function parameter 'phase0_identity' not described in 'dcss_scaler_filter_design'
Warning: drivers/gpu/drm/imx/dcss/dcss-scaler.c:270 function parameter 'nn_interpolation' not described in 'dcss_scaler_filter_design'

Fixes: 9021c317b770 ("drm/imx: Add initial support for DCSS on iMX8MQ")
Signed-off-by: Yicong Hui <yiconghui@gmail.com>
Reviewed-by: Laurentiu Palcu <laurentiu.palcu@oss.nxp.com>
Link: https://patch.msgid.link/20260406180013.2442096-1-yiconghui@gmail.com
Signed-off-by: Liu Ying <victor.liu@nxp.com>