drivers: ipm: ipm_mhu: Fix typo bug in IRQ_CONNECT

The second paramater to IRQ_CONNECT for ipm_mhu_irq_config_func_0 should
be passing the priority, instead it passed the IRQ number.  Fix this to
pass priority (which matches ipm_mhu_irq_config_func_1).

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>