Kconfig: have CCWGROUP depend on CLAW

Since the claw code calls ccwgroup_remove_ccwdev(), we need to make sure
CCWGROUP is enabled when CLAW is enabled.  Otherwise we hit fun undefined
references at build time:
ERROR: "ccwgroup_remove_ccwdev" [drivers/s390/net/claw.ko] undefined!
ERROR: "ccwgroup_probe_ccwdev" [drivers/s390/net/claw.ko] undefined!
ERROR: "ccwgroup_driver_register" [drivers/s390/net/claw.ko] undefined!
ERROR: "ccwgroup_driver_unregister" [drivers/s390/net/claw.ko] undefined!
ERROR: "ccwgroup_create_from_string" [drivers/s390/net/claw.ko] undefined!

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Frank Blaschka <frank.blaschka@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>