s390: add error handling to perf_callchain_kernel

perf_callchain_kernel stops neither when it encounters a garbage
address, nor when it runs out of space. Fix both issues using x86
version as an inspiration.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>