spi: sh-msiof: remove redundant pointer dev

The pointer dev is assigned but never read, hence it is redundant
and can be removed. Cleans up clang warning:

drivers/spi/spi-sh-msiof.c:1198:2: warning: Value stored to 'dev'
is never read

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Mark Brown <broonie@kernel.org>