pinctrl: pinctrl-single: add missing double quote

add a missing double quote for compatible property for pmx_wkup.

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Rob Landley <rob@landley.net>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Peter Ujfalusi <peter.ujfalusi@ti.com>
Cc: devicetree-discuss@lists.ozlabs.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>