pgsql: Fix incorrect comment on how BackendStatusArray is indexed

Fix incorrect comment on how BackendStatusArray is indexed

The comment was copy-pasted from the call to ProcSignalInit() in
AuxiliaryProcessMain(), which uses a similar scheme of having reserved
slots for aux processes after MaxBackends slots for backends. However,
ProcSignalInit() indexing starts from 1, whereas BackendStatusArray
starts from 0. The code is correct, but the comment was wrong.

Discussion: https://www.postgresql.org/message-id/f3ecd4cb-85ee-4e54-8278-5fabfb3a4ed0@iki.fi
Backpatch-through: v14

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/90ccc9bf90a917037f9cd451ce4c10fb9704924e

Modified Files
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src/backend/utils/activity/backend_status.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)