staging: drm/imx: Remove 300ms delay after memory reset

This has been added once, but does not seem to be necessary. Tested
on i.MX51 and i.MX6.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>