drm/arm: hdlcd: remove unused variables

The last rework left behind two unused variables:

drm/arm/hdlcd_crtc.c: In function 'hdlcd_plane_atomic_update':
drm/arm/hdlcd_crtc.c:264:13: warning: unused variable 'src_y' [-Wunused-variable]
drm/arm/hdlcd_crtc.c:264:6: warning: unused variable 'src_x' [-Wunused-variable]

This removes them.

Fixes: b2ae06ae9834 ("drm/arm: hdlcd: Use CMA helper for plane buffer address calculation")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>