ARM: imx51.dtsi: fix PATA device clock

Commit 718a350 (ARM: i.MX51: Add PATA support) adds pata support to the
imx51.dtsi file and is using clock 161. The problem is that the right
clock is 172, according to commit 5d530bb0 (ARM: i.MX5: Add PATA and SRTC
clocks).  Using the clock 172 makes things work again (and kills a nasty
system freeze).
Tested-by: Steev Klimaszewski <steev@gentoo.org>
Signed-off-by: Arnaud Patard <arnaud.patard@rtp-net.org>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/boot/dts/imx51.dtsi

@@ -474,7 +474,7 @@ pata: pata@83fe0000 {
 				compatible = "fsl,imx51-pata", "fsl,imx27-pata";
 				reg = <0x83fe0000 0x4000>;
 				interrupts = <70>;
-				clocks = <&clks 161>;
+				clocks = <&clks 172>;
 				status = "disabled";
 			};