s390/gs: add compat regset for the guarded storage broadcast control block

git commit e525f8a6
"s390/gs: add regset for the guarded storage broadcast control block"
added the missing regset to the s390_regsets array but failed to add it
to the s390_compat_regsets array.

Fixes: e525f8a6 ("add compat regset for the guarded storage broadcast control block")
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>