Documentation: Capitalize Fahrenheit in watchdog-api.rst

Capitalize "fahrenheit," a spelling mistake.

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

Documentation/watchdog/watchdog-api.rst

···
 support the GETBOOTSTATUS call.
 
 Some drivers can measure the temperature using the GETTEMP ioctl.  The
-returned value is the temperature in degrees fahrenheit::
+returned value is the temperature in degrees Fahrenheit::
 
     int temperature;
     ioctl(fd, WDIOC_GETTEMP, &temperature);