With CONFIG_DMA_API_DEBUG enabled we now get a warning when using the
mvneta driver:

  mvneta d0030000.ethernet: DMA-API: device driver frees DMA memory with
  wrong function [device address=0x000000001165b000] [size=4096 bytes]
  [mapped as page] [unmapped as single]

This is because when using the s/w buffer management, the Rx descriptor
buffer is mapped with dma_map_page but unmapped with dma_unmap_single.
This patch fixes this by using the right unmapping function.

Fixes: 562e2f46 ("net: mvneta: Improve the buffer allocation method for SWBM")
Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>