ieee1394: safer definition of empty macros

A deactivated macro, defined as "#define foo(bar)", will result in
silent corruption if somebody forgets a semicolon after a call to foo.
Replace it by "#define foo(bar) do {} while (0)" which will reveal any
respective syntax errors.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

drivers/ieee1394/video1394.c

@@ -129,7 +129,7 @@ struct file_ctx {
 #define DBGMSG(card, fmt, args...) \
 printk(KERN_INFO "video1394_%d: " fmt "\n" , card , ## args)
 #else
-#define DBGMSG(card, fmt, args...)
+#define DBGMSG(card, fmt, args...) do {} while (0)
 #endif
 
 /* print general (card independent) information */