video: fbdev: kyro: remove set but not used 'ulCoreClock'

This addresses the following gcc warning with "make W=1":

drivers/video/fbdev/kyro/STG4000InitDevice.c: In function
‘SetCoreClockPLL’:
drivers/video/fbdev/kyro/STG4000InitDevice.c:247:6: warning: variable
‘ulCoreClock’ set but not used [-Wunused-but-set-variable] // yanaijie
fixed
  247 |  u32 ulCoreClock;
      |      ^~~~~~~~~~~

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
[b.zolnierkie: minor patch summary fixup]
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200827130028.428893-1-yanaijie@huawei.com