Replace dma kernel constant

Change DMA_SUCCESS to DMA_COMPLETE

This change of variable name was introduced with the 3.13 kernel undate.
Handle return value of copy_from_user

Non-handled returns throw a warning.
Remove DMA unmap flag

The DMA_COMPL_SKIP_DEST_UNMAP is no longer used since the update to the
3.13 kernel.
Merge branch 'update-to-3.13-kernel'

These changes are necessary to get the driver to work with the
linux-xlnx kernel after the e7f96cb448b5a78 commit that merges the 3.13
Linux Kernel into master-next branch.

To get the driver to load you will need to ensure that CMA is activated
in the kernel by having the configuration in the kernel ".config" file
set as "CONFIG_DMA_CMA=y".

Tested with the linux-xlnx repo, master-next branch on commit
e8a0f03e48a0b28fb2