mfd: Fix ab3100-otp build failure

ab3100.h should include linux/workqueue.h for otp to build properly.
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/mfd/ab3100-core.c

@@ -14,7 +14,6 @@
 #include <linux/platform_device.h>
 #include <linux/device.h>
 #include <linux/interrupt.h>
-#include <linux/workqueue.h>
 #include <linux/debugfs.h>
 #include <linux/seq_file.h>
 #include <linux/uaccess.h>

include/linux/mfd/ab3100.h

@@ -6,6 +6,7 @@
  */
 
 #include <linux/device.h>
+#include <linux/workqueue.h>
 
 #ifndef MFD_AB3100_H
 #define MFD_AB3100_H