pgsql: Fix typo in pg_stat_us_to_ms()

Fix typo in pg_stat_us_to_ms()

The function converts microseconds to milliseconds, but the parameter
name used "ms".

Thinko in ac8d53dae5ae.

Author: Tatsuya Kawata <kawatatatsuya0913@gmail.com>
Discussion: /messages/by-id/CAHza6qfek15rehnA0GXMCpF2z=Gy6C+3vmcWCMVkU4JiRD8k7g@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/71fa15af591a3ec61a6bf57fee3a44a7824fba19

Modified Files
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src/backend/utils/adt/pgstatfuncs.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)