Documentation: dmaengine: Correctly describe dmatest with channel unset

Documentation: dmaengine: Correctly describe dmatest with channel unset

commit c61d7b2ef141abf81140756b45860a2306f395a2 upstream.

Currently the documentation states that channels must be configured before
running the dmatest. This has not been true since commit 6b41030fdc79
("dmaengine: dmatest: Restore default for channel"). Fix accordingly.

Fixes: 6b41030fdc79 ("dmaengine: dmatest: Restore default for channel")
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20211118100952.27268-3-daniel.thompson@linaro.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>