dmaengine: Call module_put() after device_free_chan_resources()

The module reference is taken to ensure the callbacks still exist
when they are called. If the channel holds the last reference to the
module, the module can disappear before device_free_chan_resources() is
called and would cause a call into free'd memory.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Link: https://lore.kernel.org/r/20191216190120.21374-3-logang@deltatee.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>