ARM/dts: omap3: Fix mcbsp2/3 hwmods to be able to probe the drivers for audio

Fixes the following errors:
[    2.318084] omap-mcbsp 49022000.mcbsp: invalid rx DMA channel
[    2.324432] omap-mcbsp 49024000.mcbsp: invalid rx DMA channel

Which is because we failed to link the sidetone hwmod for McBSP2/3. The
missing sidetone hwmod link will prevent omap_device_alloc() to append the
DMA resources since we - accidentally - end up having the same number of
resources provided from DT (IO/IRQ) as we have in hwmod for the McBSP ports
without the ST resources.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Benoit Cousson <b-cousson@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/boot/dts/omap3.dtsi

@@ -257,7 +257,7 @@
 			interrupt-names = "common", "tx", "rx", "sidetone";
 			interrupt-parent = <&intc>;
 			ti,buffer-size = <1280>;
-			ti,hwmods = "mcbsp2";
+			ti,hwmods = "mcbsp2", "mcbsp2_sidetone";
 		};
 
 		mcbsp3: mcbsp@49024000 {
@@ -272,7 +272,7 @@
 			interrupt-names = "common", "tx", "rx", "sidetone";
 			interrupt-parent = <&intc>;
 			ti,buffer-size = <128>;
-			ti,hwmods = "mcbsp3";
+			ti,hwmods = "mcbsp3", "mcbsp3_sidetone";
 		};
 
 		mcbsp4: mcbsp@49026000 {