ARM: imx: assert SCC gate stays enabled

The SCC clock is needed in internal boot mode and so must keep enabled.
This same issue was fixed for the pre-common-clk code in commit

	3d6e6149 (mx35: Fix boot ROM hang in internal boot mode)

Cc: John Ogness <jogness@linutronix.de>
Cc: Hans J. Koch <hjk@hansjkoch.de>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>