ARM: ux500: Use the correct name when supplying a GPIO enable pin

Correct a typo in the Device Tree source file, where instead of
specifying property 'enable-gpio', which the driver is expecting
we specified 'gpio-enable' instead.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>