f2fs: remove submit label in __submit_discard_cmd()

Complaint from Matthew Wilcox in another similar place:

	"submit?  You don't submit anything at the 'submit' label.
	it should be called 'skip' or something.  But I think this
	is just badly written and you don't need a goto at all."

Let's remove submit label for readability.

Signed-off-by: Yangtao Li <frank.li@vivo.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>