cifs: possible memory leak in xattr.

Memory is allocated irrespective of whether CIFS_ACL is configured
or not. But free is happenning only if CIFS_ACL is set. This is a
possible memory leak scenario.

Fix is:
Allocate and free memory only if CIFS_ACL is configured.

Signed-off-by: Santosh Nayak <santoshprasadnayak@gmail.com>
Reviewed-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>