broadcom-wl: fix reading fallback sprom for pci devices.

broadcom-wl: fix reading fallback sprom for pci devices.

When using the Broadcom SDK the SSB bus is emulated as an PCI bus so
the PCI bus number of the first real pci bus is increased by one. The
variable names in the nvram are created with that structure in mind. To
fix this we have ti increases the pci bus number by one. This was also
done for ssb some time ago.

This is based on a patch by nlh.
This closes #10917

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@30422 3c298f89-4303-0410-b956-a3cf2f4a3e73