ASoC: omap: Make RX51 depend on GPIOLIB due to jack usage

Since the GPIO jacks are only supported if gpiolib is built and fail to
compile otherwise add a build depedency.  This is unlikely to have any
practical impact outside of coverage testing.
Reported-by: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Mark Brown <broonie@linaro.org>
Acked-by: Jarkko Nikula <jarkko.nikula@bitmer.com>

sound/soc/omap/Kconfig

@@ -30,6 +30,7 @@ config SND_OMAP_SOC_RX51
 	select SND_OMAP_SOC_MCBSP
 	select SND_SOC_TLV320AIC3X
 	select SND_SOC_TPA6130A2
+	depends on GPIOLIB
 	help
 	  Say Y if you want to add support for SoC audio on Nokia RX-51
 	  hardware. This is also known as Nokia N900 product.