ehci: mx7: fix otg id detection

The USBNC_PHYCFG2_ACAENB bit should be cleared to enable the
OTG ID detection, not set it. When the bit is set, the ACA
Resistance Detection is enabled, which disables the OTG ID
detection, because the internal pull up is off.

Signed-off-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>