watchdog: bd96801_wdt: Add missing include for FIELD_*()

The FIELD_PREP() and FIELD_GET() macros are defined in the
linux/bitfield.h. Include this header to avoid missing the macro
definitions.

Signed-off-by: Matti Vaittinen <[e-mail]>
Reported-by: kernel test robot <[e-mail]>
Closes: https://lore.kernel.org/oe-kbuild-all/[e-mail]/
Acked-by: Guenter Roeck <[e-mail]>
Link: https://lore.kernel.org/r/ZoJhQVF-U6sSJ_Sg@fedora
Signed-off-by: Lee Jones <[e-mail]>

drivers/watchdog/bd96801_wdt.c

···
  * ROHM BD96801 watchdog driver
  */
 
+#include <linux/bitfield.h>
 #include <linux/interrupt.h>
 #include <linux/kernel.h>
 #include <linux/mfd/rohm-bd96801.h>