mbr/isohdpfx.S: correct stack for heads/sectors; revert

Heads and sectors were pushed in reverse order per isolinux.asm

bb519a9 reversed the order of heads/sectors on the stack

Signed-off-by: Gene Cumm <gene.cumm@gmail.com>

mbr/isohdpfx.S

@@ -175,12 +175,12 @@ next:
 	/* Get (C)HS geometry */
 	movb	$0x08, %ah
 	int	$0x13
-	andw	$0x3f, %cx	/* Sector count */
 	popw	%bx		/* EBIOS flag */
-	pushw	%cx		/* -16: Save sectors on the stack */
 	movzbw	%dh, %ax	/* dh = max head */
 	incw	%ax		/* From 0-based max to count */
-	pushw	%ax		/* -18: Save heads on the stack */
+	pushw	%ax		/* -16: Save heads on the stack */
+	andw	$0x3f, %cx	/* Sector count */
+	pushw	%cx		/* -18: Save sectors on the stack */
 	mulw	%cx		/* Heads*sectors -> sectors per cylinder */
 
 	pushw	%bx		/* -20: EBIOS flag */