dma-debug: fix dma_debug_add_bus() definition for !CONFIG_DMA_API_DEBUG

Impact: build fix

Fix:

 arch/x86/kvm/x86.o: In function `dma_debug_add_bus':
 (.text+0x0): multiple definition of `dma_debug_add_bus'

dma_debug_add_bus() should be a static inline function.

Cc: Joerg Roedel <joerg.roedel@amd.com>
LKML-Reference: <20090317120112.GP6159@amd.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

include/linux/dma-debug.h

@@ -83,7 +83,7 @@ extern void debug_dma_dump_mappings(struct device *dev);
 
 #else /* CONFIG_DMA_API_DEBUG */
 
-void dma_debug_add_bus(struct bus_type *bus)
+static inline void dma_debug_add_bus(struct bus_type *bus)
 {
 }