[WATCHDOG] Fix return value warning in hpwdt

The return value of smbios_scan_machine() is never used, and when it
succeeds it doesn't return anything, so just make it void.  This fixes:

    drivers/watchdog/hpwdt.c: In function 'smbios_scan_machine':
    drivers/watchdog/hpwdt.c:562: warning: control reaches end of non-void function

Signed-off-by: Roland Dreier <rolandd@cisco.com>
Acked-by: Thomas Mingarelli <Thomas.Mingarelli@hp.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>