usb: chipidea: ci13xxx_imx: remove reg_vbus

There is no need to keep a 'reg_vbus' indirection, so get rid of it.

The motivation for doing this change is that in the case of error, the current
code only sets the local reg_vbus to NULL instead of updating the private
structure 'data->reg_vbus'.

Updating only the local reg_vbus is wrong, since we currently check for
data->reg_vbus in the ci13xxx_imx_remove() function.

In order to avoid such issue, just use 'data->reg_vbus' directly.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>