dmaengine: dw-edma: Rename DebugFS dentry variables to 'dent'

Since we are about to add the eDMA channels direction support to the
debugfs module it will be confusing to have both the DebugFS directory and
the channels direction short names used in the same code. As a preparation
patch let's convert the DebugFS dentry 'dir' variables to having the
'dent' name so to prevent the confusion.

Suggested-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Tested-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Acked-By: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>