gpio: omap: simplify omap_set_gpio_dataout_x()

Both functions omap_set_gpio_dataout_reg() and
omap_set_gpio_dataout_mask() accept GPIO offset
as 'gpio' input parameter, so rename it to 'offset' and
drop usage of GPIO_BIT() macro.

Tested-by: Tony Lindgren <tony@atomide.com>
Tested-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Acked-by: Santosh Shilimkar <ssantosh@kernel.org>
Acked-by: Javier Martinez Canillas <javier@dowhile0.org>
Signed-off-by: Grygorii Strashko <grygorii.strashko@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>