staging: et131x: Match dma_alloc_ calls with dma_free_ calls

Previous update was to replace pci_alloc with dma_alloc calls. I missed
replacing the corresponding pci_free_ calls with the dma versions. Now
done. Thanks to Denis Kirjanov <kirjanov@gmail.com> for pointing this
out.

Signed-off-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>