tools/bootconfig: Fix wrong __VA_ARGS__ usage

Since printk() wrapper macro uses __VA_ARGS__ without "##" prefix, it causes
a build error if there is no variable arguments (e.g. only fmt is
specified.) To fix this error, use ##__VA_ARGS__ instead of __VAR_ARGS__.

Link: http://lkml.kernel.org/r/158108370130.2758.10893830923800978011.stgit@devnote2

Fixes: 950313eb ("tools: bootconfig: Add bootconfig command")
Reported-by: NMichael Ellerman <mpe@ellerman.id.au>
Tested-by: NMichael Ellerman <mpe@ellerman.id.au>
Signed-off-by: NMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: NSteven Rostedt (VMware) <rostedt@goodmis.org>

tools/bootconfig/include/linux/printk.h

@@ -7,7 +7,7 @@
 /* controllable printf */
 extern int pr_output;
 #define printk(fmt, ...)	\
-	(pr_output ? printf(fmt, __VA_ARGS__) : 0)
+	(pr_output ? printf(fmt, ##__VA_ARGS__) : 0)
 
 #define pr_err printk
 #define pr_warn	printk