leds: da903x: fix the building failure of incomplete type of 'work'

The leds-da903x LED driver was missing the proper #include of
linux/workqueue.h, but happened to compile on ARM due to implied
includes through other header files.

We do need the explict include on other architectures (reported at least
for x86-64).
Reported-tested-and-acked-by: NJean Delvare <khali@linux-fr.org>
Signed-off-by: NEric Miao <eric.miao@marvell.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/leds/leds-da903x.c

@@ -17,6 +17,7 @@
 #include <linux/init.h>
 #include <linux/platform_device.h>
 #include <linux/leds.h>
+#include <linux/workqueue.h>
 #include <linux/mfd/da903x.h>
 
 #define DA9030_LED1_CONTROL	0x20