vision2: Fix build due to WEIM registers name change

commit 0015de1a (MX5: Make the weim structure complete) fixed the name for
the WEIM registers in order to match with the MX51/MX53 manuals.

Fix the WEIM register for vision2 board so that it can build again.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>