staging: fsl-mc/dpio: Fix incorrect casts

The DPIO driver incorrectly assumes virtual addresses are always
64b long, which causes compiler errors when building for a 32b
platform.

Fix this by using explicit casts to uintptr_t where necessary.

Signed-off-by: Ioana Radulescu <ruxandra.radulescu@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>