mach-u300: define a dummy filter function for coh901318

All platform data has to be made conditional on
as to avoid cluttering the code with other #ifdef:s.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

arch/arm/mach-u300/include/mach/coh901318.h

@@ -102,6 +102,7 @@ struct coh901318_platform {
 	const int max_channels;
 };
 
+#ifdef CONFIG_COH901318
 /**
  * coh901318_filter_id() - DMA channel filter function
  * @chan: dma channel handle
@@ -110,6 +111,12 @@ struct coh901318_platform {
  * In dma_request_channel() it specifies what channel id to be requested
  */
 bool coh901318_filter_id(struct dma_chan *chan, void *chan_id);
+#else
+static inline bool coh901318_filter_id(struct dma_chan *chan, void *chan_id)
+{
+	return false;
+}
+#endif
 
 /*
  * DMA Controller - this access the static mappings of the coh901318 dma.