pnp: fix the fcpnp_driver declaration to only exist if CONFIG_PNP=y

Fix the fcpnp_driver declaration to only exist if CONFIG_PNP=y as it's
only accessed in that case.

The PNP=n variant was added by 30d55e71


("hisax: depend on CONFIG_PNP, not __ISAPNP__")

Fixes an unused variable warning.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Cc: Karsten Keil <kkeil@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>