reiserfs: Don't call reiserfs_get_acl() with the reiserfs lock

reiserfs_get_acl is usually not called under the reiserfs lock,
as it doesn't need it. But it happens when it is called by
reiserfs_acl_chmod(), which creates a dependency inversion against
the private xattr inodes mutexes for the given inode.

We need to call it without the reiserfs lock, especially since
it's unnecessary.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Christian Kujau <lists@nerdbynature.de>
Cc: Alexander Beregalov <a.beregalov@gmail.com>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Ingo Molnar <mingo@elte.hu>