pgsql: amcheck: Fix indentation in verify_gin.c

amcheck: Fix indentation in verify_gin.c

I forgot to reindent the code after a couple last-minute adjustments
just before committing 14ffaece0fb53fed8ddbc46d2b353e1c4834863a.

Discussion: https://postgr.es/m/45AC9B0A-2B45-40EE-B08F-BDCF5739D1E1%40yandex-team.ru

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/ec4327d106be745534592e8aff14effb716f4dc9

Modified Files
--------------
contrib/amcheck/verify_gin.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)