iio: accel: use strlcpy() instead of strncpy()

gcc-8 reports

drivers/iio/accel/st_accel_i2c.c: In function 'st_accel_i2c_probe':
./include/linux/string.h:245:9: warning: '__builtin_strncpy' specified
bound 20 equals destination size [-Wstringop-truncation]

The compiler require that the length of the dest string is greater than
the length we want to copy to make sure the dest string is
nul-terminated. We can just use strlcpy() to avoid this warning.

Signed-off-by: Xiongfeng Wang <xiongfeng.wang@linaro.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>