platform: don't return 0 from platform_get_irq[_byname]() on error

of_irq_get[_byname]() return 0 iff  irq_create_of_mapping() call fails.
Returning both  error code and 0 on failure is a sign of a misdesigned API,
it makes the failure check unnecessarily complex and error prone. We should
rely  on the platform IRQ resource in this case, not return 0,  especially
as 0 can be  a valid  IRQ resource too...

Fixes: aff008ad ("platform_get_irq: Revert to platform_get_resource if of_irq_get fails")
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
CC: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>