usb: xhci: tegra: Fix runtime PM support

Fix silly mistake when enabling runtime PM support for the Tegra XHCI
driver. If runtime PM was enabled correctly for the XHCI device, then
we should call pm_runtime_get_sync() to enable the device.

Fixes: ee9e5f4c ("usb: xhci: tegra: Add runtime PM support")
Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>