IB/hfi1: Reject a zero-length user expected buffer

IB/hfi1: Reject a zero-length user expected buffer

A zero length user buffer makes no sense and the code
does not handle it correctly.  Instead, reject a
zero length as invalid.

Fixes: 97736f36dbeb ("IB/hfi1: Validate page aligned for a given virtual addres")
Signed-off-by: Dean Luick <dean.luick@cornelisnetworks.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
Link: https://lore.kernel.org/r/167328547120.1472310.6362802432127399257.stgit@awfm-02.cornelisnetworks.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>