So far, it seemed like fans would either all be in page 0, or that
there would be one page per fan.

Turns out this was a wrong assumption. There is at least one PMBus
fan controller which supports three pages with four fans each.
Update code to handle this situation.
Reported-by: Greg Schnorr <gschnorr@cisco.com>
Tested-by: Greg Schnorr <gschnorr@cisco.com>
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
Acked-by: Greg Schnorr <gschnorr@cisco.com>