include/linux/dmapool.h: declare struct device

dmapool uses struct device in function arguments but relies on an
implicit inclusion to declare struct device causing warnings in some
configurations:

  include/linux/dmapool.h:31:7: warning: 'struct device' declared inside parameter list

Fix this by adding a struct device declaration to the file.
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/dmapool.h

@@ -14,6 +14,8 @@
 #include <asm/io.h>
 #include <asm/scatterlist.h>
 
+struct device;
+
 struct dma_pool *dma_pool_create(const char *name, struct device *dev, 
 			size_t size, size_t align, size_t allocation);