[S390] Fix build failure in __cpu_up()

The first argument to __ctl_store() should be the array to store
stuff in, not just the first element of that array.  With the
current code in __cpu_up(), mainline GCC dies with an internal
compiler error.  I didn't diagnose that further, but just fixed
the kernel bug.

Signed-off-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>