iw_cxgb4: correctly enforce the max reg_mr depth

iw_cxgb4: correctly enforce the max reg_mr depth

BugLink: http://bugs.launchpad.net/bugs/1810554
commit 7b72717a20bba8bdd01b14c0460be7d15061cd6b upstream.

The code was mistakenly using the length of the page array memory instead
of the depth of the page array.

This would cause MR creation to fail in some cases.

Fixes: 8376b86de7d3 ("iw_cxgb4: Support the new memory registration API")
Cc: stable@vger.kernel.org
Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>