spi: spidev: Remove unneeded variable

Remove unneeded variable used to store return value.

The semantic patch that makes this change is available
in scripts/coccinelle/misc/returnvar.cocci.

More information about semantic patching is available at
http://coccinelle.lip6.fr/



Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Mark Brown <broonie@kernel.org>