usb: ehci-orion: use platform_get_irq() for DT probing

Commit 77dae54a ('ARM: Kirkwood:
ehci-orion: Add device tree binding') added the Device Tree binding
for the ehci-orion driver. To achieve that with the irq, it used the
irq_of_parse_and_map() function when probed in DT-mode, and
platform_get_irq() when probed in non-DT mode.

This is not necessary: platform_get_irq() works just as fine in
DT-mode, since the conversion from DT information to 'struct resource'
is done by the generic layers of the kernel.

Therefore, this commit switches back to use just platform_get_irq().

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>