iio: chemical: sgp30: drop excess semicolon

Suggested by coccinelle / coccicheck.

CHECK   drivers/iio/chemical/sgp30.c
drivers/iio/chemical/sgp30.c:486:2-3: Unneeded semicolon

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Andreas Brauchli <a.brauchli@elementarea.net>