spi: davinci: use dma_mapping_error()

[ Upstream commit c5a2a394835f473ae23931eda5066d3771d7b2f8 ]

The correct error checking for dma_map_single() is to use
dma_mapping_error().

Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>