dmaengine: fsl-edma: Add lockdep assert for exported function

Add lockdep assert for an exported function expected to be called under
spin lock.  Since this function is called in different modules, the
lockdep assert will be self-documenting note about need for locking.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Robin Gong <yibin.gong@nxp.com>
Link: https://lore.kernel.org/r/1591877861-28156-1-git-send-email-krzk@kernel.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>