Fix build break when freezer not configured

fs/cifs/transport.c: In function 'wait_for_response':
fs/cifs/transport.c:328: error: implicit declaration of function 'wait_event_freezekillable'

Caused by commit f06ac72e

 ("cifs, freezer: add
wait_event_freezekillable and have cifs use it").  In this config,
CONFIG_FREEZER is not set.

Reviewed-by: Shirish Pargaonkar <shirishp@us.ibm.com>
CC: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>