da9030_battery: Include notifier.h

randconfig complains about:
drivers/power/da9030_battery.c:113: error: field ‘nb’ has incomplete type

because there is no direct include for notifier.h which defines
struct notifier_block.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Anton Vorontsov <anton@enomsg.org>

drivers/power/da9030_battery.c

@@ -22,6 +22,7 @@
 
 #include <linux/debugfs.h>
 #include <linux/seq_file.h>
+#include <linux/notifier.h>
 
 #define DA9030_FAULT_LOG		0x0a
 #define DA9030_FAULT_LOG_OVER_TEMP	(1 << 7)