backlight: add MODULE_ALIAS() to pwm_backlight driver

Add the missing MODULE_ALIAS() to the pwm_backlight driver.

Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: NBen Dooks <ben-linux@fluff.org>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/video/backlight/pwm_bl.c

@@ -187,3 +187,5 @@ module_exit(pwm_backlight_exit);
 
 MODULE_DESCRIPTION("PWM based Backlight Driver");
 MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:pwm-backlight");
+