IB/umem: Set correct address to the invalidation function

The invalidate range was using PAGE_SIZE instead of the computed 'end',
and had the wrong transformation of page_index due the weird
construction. This can trigger during error unwind and would cause
malfunction.

Inline the code and correct the math.

Fixes: 403cd12e ("IB/umem: Add contiguous ODP support")
Signed-off-by: Artemy Kovalyov <artemyko@mellanox.com>
Signed-off-by: Moni Shoua <monis@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>