Bill Gatliff reported the following bug when using the irq_chip facility
of the pca953x driver on a PPC platform:

BUG: scheduling while atomic: insmod/1530/0x00000002

He traced it back to an i2c transaction in pca953x_irq_set_type(), which
can be called with interrupt disabled (from __setup_irq()).  As the i2c
controller can sleep while sending a message, this qualifies as a bad
idea.

This patch moves the i2c transaction to pca953x_irq_bus_sync_unlock(),
where it is actually safe to send an i2c message.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Marc Zyngier <maz@misterjones.org>
Reported-by: Bill Gatliff <bgat@billgatliff.com>
Cc: Eric Miao <eric.y.miao@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>