ARM: imx: ehci: fix host power mask bit

This patch sets HPM (Host power mask bit) to bit 16 according to i.MX
Reference Manual. Falsely it was set to bit 8, but this controls pull-up
Impedance.

Reported-by: Michael Burkey <mdburkey@gmail.com>
Cc: Stable <stable@vger.kernel.org>
Signed-off-by: Christoph Fritz <chf.fritz@googlemail.com>
Acked-by: Eric Bénard <eric@eukrea.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>