make pnp_add_card_id() static

pnp_add_card_id() can now become static.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Cc: Bjorn Helgaas <bjorn.helgaas@hp.com>
Cc: Rene Herman <rene.herman@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>