tcg-ppc64: Fix TCG_TARGET_CALL_STACK_OFFSET

The calling convention reserves space for the 8 register parameters on
the stack, so using only 6*8=48 as the offset was wrong.  We never saw
this bug because we don't have any helpers with more than 5 parameters.
Tested-by: NTom Musta <tommusta@gmail.com>
Signed-off-by: NRichard Henderson <rth@twiddle.net>

tcg/ppc64/tcg-target.c

@@ -1408,7 +1408,7 @@ static void tcg_out_qemu_st(TCGContext *s, TCGReg data_reg, TCGReg addr_reg,
 
 /* Parameters for function call generation, used in tcg.c.  */
 #define TCG_TARGET_STACK_ALIGN       16
-#define TCG_TARGET_CALL_STACK_OFFSET 48
+#define TCG_TARGET_CALL_STACK_OFFSET ((6 + 8) * SZR)
 #define TCG_TARGET_EXTEND_ARGS       1
 
 #define FRAME_SIZE ((int) \