video: fbdev: sis: Fix set but not used warnings in init.c

video: fbdev: sis: Fix set but not used warnings in init.c

Fix "set but not used" warnings by removing the code the assign the
variables and the definition of the variables.
A register read is kept as it may have unknown side-effects.

This removes a lot of unused code - which is always a good thing to do.

v2:
  - Updated subject (Lee)

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Thomas Winischhofer <thomas@winischhofer.net>
Cc: Lee Jones <lee.jones@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201128224114.1033617-10-sam@ravnborg.org