pgsql: Standardize type of extend_by counter

Standardize type of extend_by counter

The counter of extend_by loops is mixed int and uint32. Fix by
standardizing from int to uint32, to match the extend_by variable.

Fixup for 31966b151e.

Author: Ranier Vilela <ranier.vf@gmail.com>
Reviewed-by: Gurjeet Singh <gurjeet@singh.im>
Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Discussion: /messages/by-id/CAEudQAqHG-JP-YnG54ftL_b7v6-57rMKwET_MSvEoen0UHuPig@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/9847ca2c79bef27b9bab44b2243fe951b7c62b36

Modified Files
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src/backend/storage/buffer/bufmgr.c | 6 +++---
src/backend/storage/buffer/localbuf.c | 4 ++--
2 files changed, 5 insertions(+), 5 deletions(-)