printk_once(): use bool for boolean flag

Using the type bool (instead of int) for the __print_once flag in the
printk_once() macro matches the intent of the code better, and allows the
compiler to generate smaller code; eg a typical callsite with gcc 4.3.3 on
i386:

add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-6 (-6)
function                                     old     new   delta
static.__print_once                            4       1      -3
get_cpu_vendor                               146     143      -3

Saving 6 bytes of object size per callsite by slightly improving the
readability of the source seems like a win to me.
Signed-off-by: Roland Dreier <rolandd@cisco.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/kernel.h

@@ -252,10 +252,10 @@ extern int printk_delay_msec;
  * Print a one-time message (analogous to WARN_ONCE() et al):
  */
 #define printk_once(x...) ({			\
-	static int __print_once = 1;		\
+	static bool __print_once = true;	\
 						\
 	if (__print_once) {			\
-		__print_once = 0;		\
+		__print_once = false;		\
 		printk(x);			\
 	}					\
 })