Some places return an epoch where a sync committee period is expected instead

[rupam-04]

💎 Issue

Background

@rkapka pointed out in this PR #14186
#14186 (comment)

Description

I went ahead to see in which other places the helper function compute_sync_committee_period_at_slot from CL specs
has been used as slots.ToEpoch() in the already existing implementations and asked @rkapka if they were correct or not. He said they were incorrect too and we need to wrap them using slots.SyncCommitteePeriod(). One such example would be

prysm/beacon-chain/rpc/eth/light-client/helpers.go

Line 164 in 7c81c7d

updateSignaturePeriod := slots.ToEpoch(block.Block().Slot())

Right now the fix is blocked by #14186 as the latter is working with the same file. Once it gets merged I'll start working on this fix.