Avoid recalculating pgprocno in ProcArrayAdd()

ProcArrayAdd() already calculates pgprocno via GetNumberFromPGProc()
at the top of the function, but the assignment to
arrayP->pgprocnos[index] redundantly called GetNumberFromPGProc()
again instead of reusing the local variable.  This was introduced
in commit 28f3915.

Author: Shinya Kato <shinya11.kato@gmail.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/CAOzEurTJO2aqd9ewQmo9vjCrFUAD8Lk+raujCfK5oWoLGUP_3w@mail.gmail.com

Author: shinyaaa

src/backend/storage/ipc/procarray.c

@@ -519,7 +519,7 @@ ProcArrayAdd(PGPROC *proc)
 			&ProcGlobal->statusFlags[index],
 			movecount * sizeof(*ProcGlobal->statusFlags));
 
-	arrayP->pgprocnos[index] = GetNumberFromPGProc(proc);
+	arrayP->pgprocnos[index] = pgprocno;
 	proc->pgxactoff = index;
 	ProcGlobal->xids[index] = proc->xid;
 	ProcGlobal->subxidStates[index] = proc->subxidStatus;