watchdog: hpwdt: prevent multiple "NMI occurred" messages

On platforms with no iCRU support don't print two, (possibly conflicting),
"NMI occurred" messages when the firmware is unable to source the NMI.

Please note that one of the enhancements to the v1.3.0 hpwdt driver is to panic and allow
KDUMP to succeed even on NMIs that are unknown to the platform firmware.

Signed-off-by: Naga Chumbalkar <nagananda.chumbalkar@hp.com>
Reviewed-by: Thomas Mingarelli <thomas.mingarelli@hp.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>