driver core: simplify definitions of platform_get_irq*

platform_get_irq_optional is just a wrapper for __platform_get_irq. So
rename __platform_get_irq to platform_get_irq_optional and drop
platform_get_irq_optional's previous implementation. This way there is
one function and one indirection less without loss of functionality.

Signed-off-by: Uwe Kleine-König <uwe@kleine-koenig.org>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/r/20191009093746.12095-1-uwe@kleine-koenig.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>