ext3: Don't call dquot_free_block() if we don't update anything

dquot_free_block() is called in the end of ext3_new_blocks() and updates
information of the inode structure. However, this update is not necessary
if the number of blocks we requested is equal to the number of
allocated blocks.

Signed-off-by: Kazuya Mio <k-mio@sx.jp.nec.com>
Signed-off-by: Jan Kara <jack@suse.cz>