pgsql: Fix function-header comments in planner.c

Fix function-header comments in planner.c

In b5635948ab1, a couple of function header comments weren't changed, or
weren't changed correctly, to reflect the arguments being passed into
the functions. Specifically, get_number_of_groups() had the wrong
argument name in the commit and create_grouping_paths() wasn't
updated even though the arguments had been changed.

The issue with create_grouping_paths() was noticed by Ashutosh Bapat,
while I discovered the issue with get_number_of_groups() by looking to
see if there were any similar issues from that commit.

Discussion: https://postgr.es/m/CAFjFpRcbp4702jcp387PExt3fNCt62QJN8++DQGwBhsW6wRHWA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6b960aae90164cf85cf629e0af9286f97a9e51df

Modified Files
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src/backend/optimizer/plan/planner.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)