test_regfio.c: include stdint.h before cmoka.h

test_regfio.c: include stdint.h before cmoka.h

This fix the following build failure on mips64el:
/usr/lfs/v0/rc-buildroot-test/scripts/instance-2/output/host/mips64el-buildroot-linux-uclibc/sysroot/usr/include/stdint.h:122:27: error: conflicting types for 'uintptr_t'
 typedef unsigned long int uintptr_t;
                           ^
In file included from ../source3/registry/tests/test_regfio.c:23:0:
../third_party/cmocka/cmocka.h:126:28: note: previous declaration of 'uintptr_t' was here
       typedef unsigned int uintptr_t;

Fixes:
 - http://autobuild.buildroot.org/results/bae0508e84c905dc23ad7cf1153cd1e9d8e4d734

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>