Fix PSU fan count for 9-PSU chasssis

Only 6 out of the 9 fans were previously
reported, use the get_psu_count function
to accurately get the number of PSUs
in chassis.

Change-Id: I3e227b67f928b9a2c0d82ce119a143ad0d38b040

pyghmi/ipmi/oem/lenovo/nextscale.py

@@ -228,7 +228,7 @@ fpc_sensors = {
         'type': 'Fan',
         'units': 'RPM',
         'provider': fpc_read_psu_fan,
-        'elements': 1,
+        'elementsfun': get_psu_count,
     },
     'Total Power Capacity': {
         'type': 'Power',