m32r: Fixup last __do_IRQ leftover

Somehow I managed to miss the last __do_IRQ caller when I cleanup the
remaining users. m32r is fully converted to the generic irq layer, but
I managed to not commit the conversion of __do_IRQ() to
generic_handle_irq() after compile testing the quilt series :(
Pointed-out-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Hirokazu Takata <takata@linux-m32r.org>
Cc: Paul Mundt <lethal@linux-sh.org>

arch/m32r/kernel/irq.c

@@ -80,7 +80,7 @@ asmlinkage unsigned int do_IRQ(int irq, struct pt_regs *regs)
 #ifdef CONFIG_DEBUG_STACKOVERFLOW
 	/* FIXME M32R */
 #endif
-	__do_IRQ(irq);
+	generic_handle_irq(irq);
 	irq_exit();
 	set_irq_regs(old_regs);