omap: mailbox: resolve hang issue

omap4 interrupt disable bits is different. On rx kfifo full, the mbox rx
interrupts wasn't getting disabled, and this is causing the rcm stress tests
to hang.

Signed-off-by: Hari Kanigeri <h-kanigeri2@ti.com>
Signed-off-by: Armando Uribe <x0095078@ti.com>
Signed-off-by: Fernando Guzman Lugo <fernando.lugo@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/mach-omap2/mailbox.c

@@ -193,10 +193,12 @@ static void omap2_mbox_disable_irq(struct omap_mbox *mbox,
 		omap_mbox_type_t irq)
 {
 	struct omap_mbox2_priv *p = mbox->priv;
-	u32 l, bit = (irq == IRQ_TX) ? p->notfull_bit : p->newmsg_bit;
-	l = mbox_read_reg(p->irqdisable);
-	l &= ~bit;
-	mbox_write_reg(l, p->irqdisable);
+	u32 bit = (irq == IRQ_TX) ? p->notfull_bit : p->newmsg_bit;
+
+	if (!cpu_is_omap44xx())
+		bit = mbox_read_reg(p->irqdisable) & ~bit;
+
+	mbox_write_reg(bit, p->irqdisable);
 }
 
 static void omap2_mbox_ack_irq(struct omap_mbox *mbox,