[PARISC] Work around machines which do not support chassis warnings

pdc_chassis v0.05:

Some machines seems not to implement Chassis warn support. Work around these.
Also cleanup a bit of the code.

Signed-off-by: Thibaut VARENE <varenet@parisc-linux.org>
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>