[IA64] unsigned cannot be less than 0 in sn_hwperf_ioctl()

struct sn_hwperf_ioctl_args member arg (u64) cannot be less than 0.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>