Revert "irqchip/imx-irqsteer: Constify irq_chip struct"

This reverts commit ee1e002d which is
commit e9a50f12e579a48e124ac5adb93dafc35f0a46b8 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: Ib907b82915f576c228c2b293b48ee0a9a58e9d82
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>