pgsql: Fix double assignment.

Fix double assignment.

Coverity complained about this, not without reason:

        OldMultiXactReader *state = state = pg_malloc(sizeof(*state));

(I'm surprised this is even legal C ... why is "state" in-scope
in its initialization expression?)

While at it, convert to use our newly-preferred "pg_malloc_object"
macro instead of an explicit sizeof().

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b853e644d78d99ef1779c9bf7bc3944694460aa2

Modified Files
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src/bin/pg_upgrade/multixact_read_v18.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)