[ARM] 2957/1: imx UART Error handling

Patch from Sascha Hauer

Fix error path in imx_startup.

Signed-off-by: Giancarlo Formicuccia <gformicuccia@atinno.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>