dmaengine: xilinx_dma: fix incompatible param warning in _child_probe()

In xilinx_dma_child_probe function, the nr_channels variable is
passed to of_property_read_u32() which expects an u32 return value
pointer. Modify the nr_channels variable type from int to u32 to
fix the incompatible parameter coverity warning.

Addresses-Coverity: Event incompatible_param.
Fixes: 1a9e7a03

 ("dmaengine: vdma: Add support for mulit-channel dma mode")
Signed-off-by: Shravya Kumbham <shravya.kumbham@xilinx.com>
Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Link: https://lore.kernel.org/r/1608722462-29519-3-git-send-email-radhey.shyam.pandey@xilinx.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>