cpumf/chcpumf.c: Print proper error message on non-root invocation
cpumf/chcpumf.c: Print proper error message on non-root invocation

chcpumf must be executed as root. A non-root user sees this error
message:

[tester@t35lp46 ~]$ chcpumf -m 1000
Error: /sys/module/kernel/parameters/cpum_sfb_size: Permission denied
[tester@t35lp46 ~]$

Enhance the error message and be clear about the root cause:
[tester@t35lp46 ~]$ chcpumf-new  -m 1000
Error: Must run as root
[tester@t35lp46 ~]$

Signed-off-by: Thomas Richter <8efd8ac704d21550d1708b5fda9fd8afae04d143@linux.ibm.com>
Acked-by: Sumanth Korikkar <ce55f038c56237666a10109f730271a4db066561@linux.ibm.com>
Signed-off-by: Jan Höppner <96138615ab4af0813785fa10d283f3d37eca3b78@linux.ibm.com>

ibm-s390-tools/s390-tools,ibm-s390-tools/s390-tools,ibm-s390-tools/s390-tools,ibm-s390-tools/s390-tools