f2fs: fix to check return value of f2fs_gc_range

f2fs_gc_range may return error, so its caller
f2fs_allocate_pinning_section should determine whether
to do retry based on ist return value.

Also just do f2fs_gc_range when f2fs_allocate_new_section
return -EAGAIN, and check cp error case in f2fs_gc_range.

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