ARM: dts: AM33xx: Fix properties on gpmc node

The gpmc driver is actually looking for "gpmc,num-cs" and
"gpmc,num-waitpins" properties in DT. The binding doc also states
this.
Correct the properties in the dts to provide the right values for the
gpmc driver.
Signed-off-by: NLars Poeschel <poeschel@lemonage.de>
Acked-by: NPeter Korsgaard <jacmet@sunsite.dk>
Acked-by: NPekon Gupta <pekon@ti.com>
Signed-off-by: NBenoit Cousson <benoit.cousson@linaro.org>

arch/arm/boot/dts/am33xx.dtsi

@@ -409,8 +409,8 @@
 			ti,hwmods = "gpmc";
 			reg = <0x50000000 0x2000>;
 			interrupts = <100>;
-			num-cs = <7>;
-			num-waitpins = <2>;
+			gpmc,num-cs = <7>;
+			gpmc,num-waitpins = <2>;
 			#address-cells = <2>;
 			#size-cells = <1>;
 			status = "disabled";