imx: woodburn: Remove reference to gdata

The global_data pointer (gd) has already been set before board_init_f()
is called. We should not assign it again. We should also not use gdata since
it is going away.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Stefano Babic <sbabic@denx.de>