gpio: omap: simplify omap_gpio_get_direction()

Architectures are single-copy atomic, which means that simply reading
a register is an inherently atomic operation.  There is no need to
take a spinlock here.

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>