spi: mark device nodes only in case of successful instantiation

Instantiated SPI device nodes are marked with OF_POPULATE. This was
introduced in bd6c1644. On unloading, loaded device nodes will of course
be unmarked. The problem are nodes that fail during initialisation: If a
node fails, it won't be unloaded and hence not be unmarked.

If a SPI driver module is unloaded and reloaded, it will skip nodes that
failed before.

Skip device nodes that are already populated and mark them only in case
of success.

Note that the same issue exists for I2C.

Fixes: bd6c1644 ("spi: Mark instantiated device nodes with OF_POPULATE")
Signed-off-by: Ralf Ramsauer <ralf@ramses-pyramidenbau.de>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org