f2fs: fix to handle error paths of {new,change}_curseg()

{new,change}_curseg() may return error in some special cases,
error handling should be did in their callers, and this will also
facilitate subsequent error path expansion in {new,change}_curseg().

Signed-off-by: Zhiguo Niu <zhiguo.niu@unisoc.com>
Signed-off-by: Chao Yu <chao@kernel.org>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>