usb: phy: tegra: Add error handling & clean up.

Check return values from all GPIO APIs and handle errors accordingly.

Remove the call to clk_disable_unprepare(); this function does not
prepare or enable the clock, so the error path should not disable or
unprepare it.

Signed-off-by: Venu Byravarasu <vbyravarasu@nvidia.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>