Both of_dma_nbcells field of the of_dma_controller and the args_count field of
the dma_spec are initialized by parsing the #dma-cells attribute of their device
tree node. So if the device tree nodes of a DMA controller and the dma_spec
match this means that of_dma_nbcells and args_count will also match. So the
second test in the of_dma_find_controller loop is redundant because given the
first test yields true the second test will also yield true. So we can safely
remove the test whether of_dma_nbcells matches args_count. Since this was the
last user of the of_dma_nbcells field we can remove it altogether.