dmaengine: Refactor devm_dma_request_chan() for readability

dmaengine: Refactor devm_dma_request_chan() for readability

Yes, while it's a bit longer in terms of LoCs, it's more readable
when we use the usual patter to check for errors, and not for
a success). This eliminates unneeded assignment and moves the
needed one closer to its user which is better programming pattern
because it allows avoiding potential errors in case the variable
is getting reused. Also note that the same pattern have been used
already in dmaenginem_async_device_register().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260109173718.3605829-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>