quota: Move down dqptr_sem read after initializing default warn[] type at __dquot_alloc_space().

sb->s_dqopt->dqptr_sem is used to serialize ops using pointers from inode to
dquots.  But for __dquot_alloc_space(), it could be safely moved down after the
default warn[] array got initialized.

Signed-off-by: Jie Liu <jeff.liu@oracle.com>
Signed-off-by: Jan Kara <jack@suse.cz>