dmaengine: Add dma_get_slave_caps() inline stub when !CONFIG_DMA_ENGINE

Commit 0d5484b1 ("dmaengine: Move dma_get_slave_caps()
implementation to dmaengine.c") turned the inline dma_get_slave_caps()
function into an external function without adding an inline stub for the
cases where CONFIG_DMA_ENGINE isn't set. This breaks compilation of
drivers using the DMA engine API when CONFIG_DMA_ENGINE isn't set.

Add an inline stub to fix compilation.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Fixes: 0d5484b1 ("dmaengine: Move dma_get_slave_caps() implementation to dmaengine.c")
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

include/linux/dmaengine.h

@@ -758,8 +758,6 @@ static inline struct dma_async_tx_descriptor *dmaengine_prep_dma_sg(
 			src_sg, src_nents, flags);
 }
 
-int dma_get_slave_caps(struct dma_chan *chan, struct dma_slave_caps *caps);
-
 static inline int dmaengine_terminate_all(struct dma_chan *chan)
 {
 	if (chan->device->device_terminate_all)
@@ -1048,6 +1046,7 @@ struct dma_chan *dma_request_slave_channel_reason(struct device *dev,
 						  const char *name);
 struct dma_chan *dma_request_slave_channel(struct device *dev, const char *name);
 void dma_release_channel(struct dma_chan *chan);
+int dma_get_slave_caps(struct dma_chan *chan, struct dma_slave_caps *caps);
 #else
 static inline struct dma_chan *dma_find_channel(enum dma_transaction_type tx_type)
 {
@@ -1082,6 +1081,11 @@ static inline struct dma_chan *dma_request_slave_channel(struct device *dev,
 static inline void dma_release_channel(struct dma_chan *chan)
 {
 }
+static inline int dma_get_slave_caps(struct dma_chan *chan,
+				     struct dma_slave_caps *caps)
+{
+	return -ENXIO;
+}
 #endif
 
 /* --- DMA device --- */