s390/ipl: add missing IPL_TYPE_ECKD_DUMP case to ipl_init()

Add missing IPL_TYPE_ECKD_DUMP case to ipl_init() creating
ECKD ipl device attribute group similar to IPL_TYPE_ECKD case.
Commit e2d2a2968f2a ("s390/ipl: add eckd dump support") should
have had it from the beginning.

Fixes: e2d2a2968f2a ("s390/ipl: add eckd dump support")
Signed-off-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>