dmaengine: sun6i: Fix impossible settings of burst and bus width

In the commit 1f9cd915 ("dmaengine: sun6i: Fix memcpy operation"),
the signed values returned by convert_burst() and convert_buswidth()
were stored in an unsigned value.
Then, these values were considered as errors when non null.

As a result, DMA transfers were rejected when the burst or buswidth
had values different from 1, as 8 for the burst or 4 for the bus width.
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/sun6i-dma.c

@@ -281,25 +281,25 @@ static inline int sun6i_dma_cfg_lli(struct sun6i_dma_lli *lli,
 				    dma_addr_t dst, u32 len,
 				    struct dma_slave_config *config)
 {
-	u8 src_width, dst_width, src_burst, dst_burst;
+	s8 src_width, dst_width, src_burst, dst_burst;
 
 	if (!config)
 		return -EINVAL;
 
 	src_burst = convert_burst(config->src_maxburst);
-	if (src_burst)
+	if (src_burst < 0)
 		return src_burst;
 
 	dst_burst = convert_burst(config->dst_maxburst);
-	if (dst_burst)
+	if (dst_burst < 0)
 		return dst_burst;
 
 	src_width = convert_buswidth(config->src_addr_width);
-	if (src_width)
+	if (src_width < 0)
 		return src_width;
 
 	dst_width = convert_buswidth(config->dst_addr_width);
-	if (dst_width)
+	if (dst_width < 0)
 		return dst_width;
 
 	lli->cfg = DMA_CHAN_CFG_SRC_BURST(src_burst) |