USB: ehci-tegra: don't call set_irq_flags(IRQF_VALID)

This call is not needed; the IRQ controller should (and does) set up
interrupts correctly. set_irq_flags() isn't exported to modules, to
this also fixes compilation of ehci-tegra.c as a module.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>