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 <mazziesaccount@gmail.com>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202406300817.hcJ9VtLf-lkp@intel.com/Acked-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/ZoJhQVF-U6sSJ_Sg@fedoraSigned-off-by: Lee Jones <lee@kernel.org>

drivers/watchdog/bd96801_wdt.c

@@ -5,6 +5,7 @@
  * ROHM BD96801 watchdog driver
  */
 
+#include <linux/bitfield.h>
 #include <linux/interrupt.h>
 #include <linux/kernel.h>
 #include <linux/mfd/rohm-bd96801.h>