twl4030-usb: rename twl4030_driver to twl4030_usb_driver.

The i2c_driver in twl4030-core.c and platform_driver of twl4030-usb.c
both has the name twl4030_driver. This leads to unnecessary confusion.

So rename the usb platform_driver appropriately to:
twl4030_usb_driver.

Signed-off-by: Jagadeesh Bhaskar Pakaravoor <j-pakaravoor@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>