powerpc/pseries/svm: Drop unused align argument in alloc_shared_lppaca() function

Argument "align" in alloc_shared_lppaca() was unused inside the
function. Let's drop it and update code comment for page alignment.

Signed-off-by: Satheesh Rajendran <sathnaga@linux.vnet.ibm.com>
Reviewed-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Reviewed-by: Laurent Dufour <ldufour@linux.ibm.com>
[mpe: Massage comment wording/formatting]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200612142953.135408-1-sathnaga@linux.vnet.ibm.com