s390/sclp: avoid compile warning in sclp_pci_report

Fix the initialization of a local variable to remove this warning:

All warnings (new ones prefixed by >>):

   drivers/s390/char/sclp_pci.c: In function 'sclp_pci_report':
>> drivers/s390/char/sclp_pci.c:127:9: warning: missing braces around initializer [-Wmissing-braces]
     struct sclp_req req = {0};
            ^
   drivers/s390/char/sclp_pci.c:127:9: warning: (near initialization for 'req.list') [-Wmissing-braces]

Fixes: 12283a40 "s390/sclp: add error notification command"
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>