paride: fix up build warning on mips platforms

paride: fix up build warning on mips platforms

MIPS include files define "PC" so when building the paride driver the
following build warning shows up:

	rivers/block/paride/bpck.c:32: warning: "PC" redefined

Fix this by undefining PC before redefining it as is done for other
defines in this driver.

Cc: Tim Waugh <tim@cyberelk.net>
Acked-by: Jens Axboe <axboe@kernel.dk>
Link: https://lore.kernel.org/r/20211130084626.3215987-1-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>