cifs: don't call cifs_new_fileinfo unless cifs_open succeeds

It's currently possible for cifs_open to fail after it has already
called cifs_new_fileinfo. In that situation, the new fileinfo will be
leaked as the caller doesn't call fput. That in turn leads to a busy
inodes after umount problem since the fileinfo holds an extra inode
reference now. Shuffle cifs_open around a bit so that it only calls
cifs_new_fileinfo if it's going to succeed.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-and-Tested-by: Suresh Jayaraman <sjayaraman@suse.de>