Fix this warning:

arch/s390/appldata/appldata_net_sum.c: In function 'appldata_get_net_sum_data':
arch/s390/appldata/appldata_net_sum.c:89: warning: initialization from incompatible pointer type

which was introduced with be1f3c2c
"net: Enable 64-bit net device statistics on 32-bit architectures"
Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>