UBI: fix missing brace control flow

[ Upstream commit b388e6a7a6ba988998ddd83919ae8d3debf1a13d ]

commit 0e707ae79ba3 ("UBI: do propagate positive error codes up") seems
to have produced an unintended change in the control flow here.

Completely untested, but it looks obvious.

Caught by Coverity, which didn't like the indentation. CID 1271184.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>