Improve some code format in gist.c

Author: Tender Wang
Discussion: https://postgr.es/m/CAHewXNmD=K7XmsHq=L1SyyzZYvwU4oaMG9EKSSMe4OrXfykLzg@mail.gmail.com

Author: michaelpq

src/backend/access/gist/gist.c

@@ -43,7 +43,7 @@ static void gistprunepage(Relation rel, Page page, Buffer buffer,
 
 
 #define ROTATEDIST(d) do { \
-	SplitPageLayout *tmp=(SplitPageLayout*)palloc0(sizeof(SplitPageLayout)); \
+	SplitPageLayout *tmp = (SplitPageLayout *) palloc0(sizeof(SplitPageLayout)); \
 	tmp->block.blkno = InvalidBlockNumber;	\
 	tmp->buffer = InvalidBuffer;	\
 	tmp->next = (d); \