MIPS: ralink: Fix bad config symbol in PCI makefile.

A wrong symbol is referenced by commit 187c26dd

 ("MIPS: ralink: add rt2880
pci driver"). Fix this by changing it to the correct symbol.

Signed-off-by: John Crispin <blogic@openwrt.org>
Reported-by: Paul Bolle <pebolle@tiscali.nl>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9298/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>