s390/sclp: replace uninitialized early_event_mask_sccb variable with sccb_early

s390/sclp: replace uninitialized early_event_mask_sccb variable with sccb_early

Commit "s390/sclp: Consolidate early sclp init calls to sclp_early_detect()"
(7b50da53f6ad2048241bef232bfc22a132a40283) replaced the sclp_event_mask_early()
with sclp_set_event_mask().  The early_event_mask_sccb variable is no longer
initialized but is still used in sclp_has_linemode() and sclp_has_vt220().

Replace early_event_mask_sccb with the sccb_early variable in both
functions.

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>