video: fbdev: gbefb: Fix set but not used warning

The variable "x" was set but never used.
Drop the redundant assignments.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201206190247.1861316-11-sam@ravnborg.org