video: fbdev: radeonfb: remove set but not used variable '‘cSync’'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/video/fbdev/aty/radeon_base.c: In function
‘radeonfb_set_par’:
drivers/video/fbdev/aty/radeon_base.c:1653:48: warning: variable
‘cSync’ set but not used [-Wunused-but-set-variable]

It is never used, and so can be removed.

Signed-off-by: yu kuai <yukuai3@huawei.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: zhengbin <zhengbin13@huawei.com>
Cc: yi.zhang <yi.zhang@huawei.com>
[b.zolnierkie: patch summary fixups]
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200119121730.10701-4-yukuai3@huawei.com