[MIPS] Misc fixes for plat_irq_dispatch functions

 o adds missing ST0_IM masks, which caused the logging of valid interrupts
   as spurious
 o stops pnx8550 to log every interrupt as spurious
 o adds cause register masks for ip22/ip32, which caused handling of masked
   interrupts
 o removes some superfluous parentheses in the SNI interrupt code

Signed-Off-By: Thiemo Seufer <ths@networkno.de>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/sgi-ip32/ip32-irq.c b/arch/mips/sgi-ip32/ip32-irq.c
index 8c450d9..fb9da9a 100644
--- a/arch/mips/sgi-ip32/ip32-irq.c
+++ b/arch/mips/sgi-ip32/ip32-irq.c
@@ -454,7 +454,7 @@
 
 asmlinkage void plat_irq_dispatch(void)
 {
-	unsigned int pending = read_c0_cause();
+	unsigned int pending = read_c0_status() & read_c0_cause();
 
 	if (likely(pending & IE_IRQ0))
 		ip32_irq0();