power: reset: piix4: add missing MODULE_DESCRIPTION() macro

make allmodconfig && make W=1 C=1 reports:
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/power/reset/piix4-poweroff.o

Add the missing invocation of the MODULE_DESCRIPTION() macro.

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Link: https://lore.kernel.org/r/20240608-md-drivers-power-reset-v1-1-08dbc1a546a2@quicinc.com


Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>