ceph: fix SEEK_CUR, SEEK_SET regression

Commit 06222e491e663dac939f04b125c9dc52126a75c4 got the if wrong so that
it always evaluates as true.  This is semantically harmless, but makes
SEEK_CUR and SEEK_SET needlessly query the server.

Rewrite the if to explicitly enumerate the cases we DO need a valid i_size
to make this code less fragile.

Reported-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/file.c

@@ -797,7 +797,8 @@ static loff_t ceph_llseek(struct file *file, loff_t offset, int origin)
 
 	mutex_lock(&inode->i_mutex);
 	__ceph_do_pending_vmtruncate(inode);
-	if (origin != SEEK_CUR || origin != SEEK_SET) {
+
+	if (origin == SEEK_END || origin == SEEK_DATA || origin == SEEK_HOLE) {
 		ret = ceph_do_getattr(inode, CEPH_STAT_CAP_SIZE);
 		if (ret < 0) {
 			offset = ret;