platform/x86: intel_punit_ipc: Avoid error message when retrieving IRQ
Since the commit
7723f4c5ecdb ("driver core: platform: Add an error message to platform_get_irq*()")
the platform_get_irq() started issuing an error message which is not
what we want here.
Switch to platform_get_irq_optional() to have only warning message
provided by the driver.
Fixes: 7723f4c5ecdb ("driver core: platform: Add an error message to platform_get_irq*()")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>