In the SetPortFeature/USB_PORT_FEAT_ENABLE case, ehci_hub_control()
would read from status_reg, modify the value, and write the result back to
status_reg. This would clear any bits in PORT_RWC_BITS that were set in
the register. Fix this by masking these bits off before the write.

This is logically the same change as 6d5f89c "USB: EHCI: remove
PORT_RWC_BITS when clearing USB_PORT_FEAT_ENABLE", but applied to the
Tegra driver rather than the USB core.
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>