drm/client: Remove pitch from struct drm_client_buffer

drm/client: Remove pitch from struct drm_client_buffer

Only the client-buffer setup uses the pitch field from struct
drm_client_buffer. Remove the field and pass the value among setup
helpers.

Clients that need the pitch should rather look at the framebuffer's
pitches[0] directly.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Tested-by: Francesco Valla <francesco@valla.it>
Link: https://patch.msgid.link/20251027121042.143588-2-tzimmermann@suse.de