Parameter use_msi was used to enable msi irq on usb338x chips, it was
enabled by default.

There is no reason to prefer non-msi irq on usb338x, and it falls back
to non msi on error.

Therefore remove this option.
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>