gpio: omap: simplify get_multiple()

There is no reason to have helper functions to read the datain and
dataout registers when they are only used in one location.  Simplify
this code to make it more readable.

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>