Flight Log previous hash match comparing current signature with previous signature

[abrbhat]

In submit flight log endpoint: https://github.com/iSpirt/digital-sky-api/blob/3ba72f51a883345f28d311c03a0dd2fb12eff0f5/src/main/java/com/ispirit/digitalsky/service/FlightLogServiceImpl.java#L41

It seems that previous flightLogEntry.signature is incorrectly being compared to current flightLogEntry.signature. Instead, previous flightLogEntry.signature should be compared to current flightLogEntry.flightLog.previousLogHash.

@sidd-shetty @sidhantgoel @suraj-shanbhag @CharanSahaj