f2fs: remove unneeded check code with option in f2fs_remount

Because we have checked the contrary condition in case of "if" judgment, we do
not need to check the condition again in case of "else" judgment. Let's remove
it.

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>