hwmon: (lm70) Remove redundant spi_set_drvdata

Driver core sets driver data to NULL upon failure or remove.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Cc: Kaiwan N Billimoria <kaiwan@designergraphix.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>