selftests: vm: pkeys: use the correct huge page size

The huge page size can vary across architectures.  This will ensure that
the correct huge page size is used when accessing the hugetlb controls
under sysfs.  Instead of using a hardcoded page size (i.e.  2MB), this now
uses the HPAGE_SIZE macro which is arch-specific.

Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Dave Hansen <dave.hansen@intel.com>
Cc: "Desnes A. Nunes do Rosario" <desnesn@linux.vnet.ibm.com>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Suchanek <msuchanek@suse.de>
Cc: Shuah Khan <shuah@kernel.org>
Link: http://lkml.kernel.org/r/66882a5d6e45c73c3a52bc4aef9754e48afa4f88.1585646528.git.sandipan@linux.ibm.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>