ARM: iop13xx: fix msi support with sparse IRQ

patch 37ebbcff

 ("arm: iop13xx: Use sparse irqs for MSI") moved
iop13xx over to sparse IRQ support, but this broke the build for the
msi.c file, which now has to include mach/irqs.h itself.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/12285212.fBJyVfk69p@wuerfel
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>