Documentation/watchdog/hpwdt: Fix Reference

The IPMI documentation moved to Documentation/driver-api/ipmi.rst.
Update reference to reflect new location.

Signed-off-by: Jerry Hoemann <[e-mail]>
Reviewed-by: Guenter Roeck <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Corbet <[e-mail]>

Documentation/watchdog/hpwdt.rst

···
  NOTE:
        More information about watchdog drivers in general, including the ioctl
        interface to /dev/watchdog can be found in
-       Documentation/watchdog/watchdog-api.rst and Documentation/IPMI.txt.
+       Documentation/watchdog/watchdog-api.rst and Documentation/driver-api/ipmi.rst
 
  Due to limitations in the iLO hardware, the NMI pretimeout if enabled,
  can only be set to 9 seconds.  Attempts to set pretimeout to other