quota: Fix issuing of warnings from dquot_transfer

__dquot_transfer accidentally called flush_warnings for a wrong set of
dquots which could result in quota warnings being issued with a wrong
identification. Also when operation fails because of EDQUOT, there's no
need check for issuing information message about user getting below limits
(no transfer has actually happened).

Signed-off-by: Jan Kara <jack@suse.cz>