gpio: omap: clean up omap_gpio_restore_context()

Use local variables to store the base iomem address and regs table
pointer like omap_gpio_init_context() does. Not only does this make
the function neater, it also avoids unnecessary reloads of the same
data multiple times.

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>