ignore erroneous vflash error

This is caused by ipmi-sensors giving classifying vFlash as critical and
Absent/Failed when in fact there is no issue. Technically a freeipmi bug that
misclassifies 'OEM Event = 0021h' as Absent/Failed, so we just disable it.

77  | vFlash | Module/Board | Critical | N/A | N/A| 'Absent' 'Failed'

Change-Id: I2867c557ad1444c1307aa1848c5d7cf77b37b2f0