This drops the "ti-" prefix from the module name. It makes the module name
consistent with other iio ti-ads* drivers and it makes the driver work
with device tree (the spi subsystem drops the "ti," prefix when matching
compatible strings from device tree).

Tested working on LEGO MINDSTORMS EV3 with the following device tree node:

	adc@3 {
		compatible = "ti,ads7957";
		reg = <3>;
		#io-channel-cells = <1>;
		spi-max-frequency = <10000000>;
		vref-supply = <&adc_ref>;
	};
Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>