softirq: use const char * const for softirq_to_name, whitespace neatening

Reduce data size a little.
Reduce checkpatch noise.

$ size kernel/softirq.o*
   text	   data	    bss	    dec	    hex	filename
  11554	   6013	   4008	  21575	   5447	kernel/softirq.o.new
  11474	   6093	   4008	  21575	   5447	kernel/softirq.o.old

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/interrupt.h

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index db43b58..0053add 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -360,7 +360,7 @@
 /* map softirq index to softirq name. update 'softirq_to_name' in
  * kernel/softirq.c when adding a new softirq.
  */
-extern char *softirq_to_name[NR_SOFTIRQS];
+extern const char * const softirq_to_name[NR_SOFTIRQS];
 
 /* softirq mask and active fields moved to irq_cpustat_t in
  * asm/hardirq.h to get better cache usage.  KAO