leds: Fix sparse warnings in leds-h1940 driver

Fixes the following sparse errors:
drivers/leds/leds-h1940.c:26:6: warning: symbol 'h1940_greenled_set' was not declared. Should it be static?
drivers/leds/leds-h1940.c:55:6: warning: symbol 'h1940_redled_set' was not declared. Should it be static?
drivers/leds/leds-h1940.c:85:6: warning: symbol 'h1940_blueled_set' was not declared. Should it be static?

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Richard Purdie <rpurdie@rpsys.net>