spi: ep93xx: Drop unused variable

My previous patch leaves a dangling variable in the driver.
get rid of it.

Fixes: 06a391b1621e ("spi: ep93xx: Convert to use CS GPIO descriptors")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>