staging: fsl-mc: bus: Drop warning

When updating the irq_chip and msi_domain_ops, the code checkes for
already present functions.
When more then one ITS controller are present in the system,
irq_chip and msi_domain_ops got already set and a warning is invoked.

This patch deletes the warning, as the funtions are just already set to
the needed callbacks.

Signed-off-by: Matthias Brugger <mbrugger@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>