iw_cxgb4: correctly enforce the max reg_mr depth

BugLink: https://bugs.launchpad.net/bugs/1790620

commit 7b72717a 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: 8376b86d ("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: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/infiniband/hw/cxgb4/mem.c

@@ -926,7 +926,7 @@ static int c4iw_set_page(struct ib_mr *ibmr, u64 addr)
 {
 	struct c4iw_mr *mhp = to_c4iw_mr(ibmr);
 
-	if (unlikely(mhp->mpl_len == mhp->max_mpl_len))
+	if (unlikely(mhp->mpl_len == mhp->attr.pbl_size))
 		return -ENOMEM;
 
 	mhp->mpl[mhp->mpl_len++] = addr;