i2c: mux: pca954x: Return error if irq_create_mapping fails

irq_create_mapping can return an error, report error to log and return.
Cleanup will occur in the probe function when an error is returned.

Suggested-by: Peter Rosin <peda@axentia.se>
Acked-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Phil Reid <preid@electromag.com.au>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>