dmaengine: qcom: hidma: no need to check return value of debugfs_create functions

When calling debugfs functions, there is no need to ever check the
return value.  The function can work or not, but the code logic should
never do something different based on this.

Also, because there is no need to save the file dentry, remove the
variables that were saving them as they were never even being used once
set.

Cc: Sinan Kaya <okaya@kernel.org>
Cc: Andy Gross <agross@kernel.org>
Cc: David Brown <david.brown@linaro.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Vinod Koul <vkoul@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-arm-msm@vger.kernel.org
Cc: dmaengine@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Sinan Kaya <okaya@kernel.org>
Signed-off-by: Vinod Koul <vkoul@kernel.org>