target/s390x: change PSW_SHIFT_KEY

Such shifts are usually used to easily extract the PSW KEY from the PSW
mask, so let's avoid the confusing offset of 4.

Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20170614133819.18480-2-david@redhat.com>
Signed-off-by: Richard Henderson <rth@twiddle.net>
2 files changed