drm/komeda: remove set but not used variable 'kcrtc'

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

drivers/gpu/drm/arm/display/komeda/komeda_plane.c: In function komeda_plane_atomic_check:
drivers/gpu/drm/arm/display/komeda/komeda_plane.c:49:22: warning: variable kcrtc set but not used [-Wunused-but-set-variable]

It is never used since introduction in
commit 9e560309

 ("drm/komeda: Add komeda_plane/plane_helper_funcs")

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: James Qian Wang (Arm Technology China) <james.qian.wang@arm.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>