[COMMITTERS] pgsql: Revert unintentional change in increasing usage count duringpin

Revert unintentional change in increasing usage count during pin of buffers,
this makes buffer access strategy have no effect.
Change was a part of commit 48354581a49c30f5757c203415aa8412d85b0f70 during 9.6
release cycle, so backpath to 9.6

Reported-by: Jim Nasby
Author: Alexander Korotkov
Reviewed-by: Jim Nasby, Andres Freund

https://commitfest.postgresql.org/13/1029/

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/9cf6033281fdaf938b826545a643f951086d8671

Modified Files
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src/backend/storage/buffer/bufmgr.c | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)