sparc64: Fix mapping of 64k pages with MAP_FIXED

An incorrect huge page alignment check caused
mmap failure for 64K pages when MAP_FIXED is used
with address not aligned to HPAGE_SIZE.

Orabug: 25885991

Fixes: dcd1912d ("sparc64: Add 64K page size support")
Signed-off-by: Nitin Gupta <nitin.m.gupta@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>