pgsql: Fix deprecated-by-C-spec usage: storage class should come before

Log Message:
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Fix deprecated-by-C-spec usage: storage class should come before const
decoration. Zdenek Kotala

Modified Files:
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pgsql/src/interfaces/ecpg/ecpglib:
prepare.c (r1.22 -> r1.23)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/ecpglib/prepare.c?r1=1.22&r2=1.23)