[S390] module: fix memory leak in s390 module loader

The s390 version of module_frob_arch_sections allocates additional
syminfos for got and plt offsets. These syminfos are freed on
sucessful module load. If the module fails to load (e.g. missing
dependency when using insmod instead of modprobe) this area is not
freed.
This patch lets module_free free this area. Please note, we have to
set the pointer to NULL since module_free is called several times
from the generic code.

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