hwmon: (i5k_amb) Remove redundant platform_set_drvdata()

Commit 0998d063

 (device-core: Ensure drvdata = NULL when no
driver is bound) removes the need to set driver data field to
NULL.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Cc: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>