Fix build when CONFIG_W1_MASTER_GPIO=m b exporting "allnodes"

ERROR: "allnodes" [drivers/w1/masters/w1-gpio.ko] undefined!

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
[grant.likely: allnodes is too generic; rename to of_allnodes]
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Cc: Ville Syrjala <syrjala@sci.fi>