s390/sysinfo: allow compiler warnings again

Allow compiler warnings again for the sysinfo file. Compiler warnings
were disabled when the bogomips calculation with math-emu code was
introduced ("[S390] Calibrate delay and bogomips.").
Since that code is gone, we can enable warnings again.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>