spi: sh-msiof: fix deferred probing

Since commit 9ec36caf ("of/irq: do irq resolution in platform_get_irq")
platform_get_irq() can return -EPROBE_DEFER. However, the driver overrides
an error returned by that function with -ENOENT which breaks the deferred
probing. Propagate upstream an error code returned by platform_get_irq()
and remove the bogus "platform" from the error message, while at it...

Fixes: 9ec36caf ("of/irq: do irq resolution in platform_get_irq")
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Mark Brown <broonie@kernel.org>