backlight: Declare backlight_types[] const

Since backlight_types[] isn't modified, let's declare it const.  That
was probably the intention of the author of commit bb7ca747
("backlight: add backlight type"), via which the "const char const *"
construct was introduced.  The duplicate const was detected by sparse.
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: Matthew Garrett <mjg@redhat.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Cc: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/video/backlight/backlight.c

@@ -19,7 +19,7 @@
 #include <asm/backlight.h>
 #endif
 
-static const char const *backlight_types[] = {
+static const char *const backlight_types[] = {
 	[BACKLIGHT_RAW] = "raw",
 	[BACKLIGHT_PLATFORM] = "platform",
 	[BACKLIGHT_FIRMWARE] = "firmware",