gpio: omap: simplify get() method

omap_gpio_get() calls omap_get_gpio_datain() or omap_get_gpio_dataout()
to read the GPIO state. These two functions are only called from this
method, so they don't add much value.  Move their contents into
omap_gpio_get() method and simplify.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>