dma: mmp_pdma: Fix the #dma-channels DT property documentation

The property is optional and defaults to 32. Document it as such.

Cc: devicetree@vger.kernel.org
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: NVinod Koul <vinod.koul@intel.com>

Documentation/devicetree/bindings/dma/mmp-dma.txt

 * MARVELL MMP DMA controller
 
 Marvell Peripheral DMA Controller
-Used platfroms: pxa688, pxa910, pxa3xx, etc
+Used platforms: pxa688, pxa910, pxa3xx, etc
 
 Required properties:
 - compatible: Should be "marvell,pdma-1.0"
 - reg: Should contain DMA registers location and length.
 - interrupts: Either contain all of the per-channel DMA interrupts
 		or one irq for pdma device
-- #dma-channels: Number of DMA channels supported by the controller.
+
+Optional properties:
+- #dma-channels: Number of DMA channels supported by the controller (defaults
+  to 32 when not specified)
 
 "marvell,pdma-1.0"
-Used platfroms: pxa25x, pxa27x, pxa3xx, pxa93x, pxa168, pxa910, pxa688.
+Used platforms: pxa25x, pxa27x, pxa3xx, pxa93x, pxa168, pxa910, pxa688.
 
 Examples:
 
@@ -45,7 +48,7 @@ pdma: dma-controller@d4000000 {
 
 
 Marvell Two Channel DMA Controller used specifically for audio
-Used platfroms: pxa688, pxa910
+Used platforms: pxa688, pxa910
 
 Required properties:
 - compatible: Should be "marvell,adma-1.0" or "marvell,pxa910-squ"