x86/pkeys: Clean up arch_set_user_pkey_access() declaration

arch_set_user_pkey_access() was declared two times in the header.

Remove the 2nd declaration.

Suggested-by: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lkml.kernel.org/r/20220331180554.2945884-1-ira.weiny@intel.com