[S390] sparse: fix sparse warnings with __user pointers

Use __force to quiet sparse warnings about user address space.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --cc arch/s390/kernel/compat_signal.c
Simple merge

diff --cc arch/s390/kernel/traps.c
Simple merge

diff --cc arch/s390/lib/uaccess_pt.c
Simple merge