f2fs: remove redundant assignment to variable err

The variable err is being assigned a value zero and then the following
goto page_hit reassigns err a new value. The zero assignment is redundant
and can be removed.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
[Jaegeuk Kim: clean up braces and if condition, suggested by Dan Carpenter]
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>