dmaengine: dw-edma: Stop checking debugfs_create_*() return value

First of all they never return NULL. So checking their return value for
being not NULL just pointless. Secondly the DebugFS subsystem is designed
in a way to be used as simple as possible. So if one of the
debugfs_create_*() method in a hierarchy fails, the following methods will
just silently return the passed erroneous parental dentry. Finally the
code is supposed to be working no matter whether anything DebugFS-related
fails. So in order to make code simpler and DebugFS-independent let's drop
the debugfs_create_*() methods return value checking in the same way as
the most of the kernel drivers do.

Note in order to preserve some memory space we suggest to skip the DebugFS
nodes initialization if the file system in unavailable.

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>