iio: chemical: sps30_serial: fix buffer size in sps30_serial_read_meas()

iio: chemical: sps30_serial: fix buffer size in sps30_serial_read_meas()

sizeof(num) evaluates to sizeof(size_t) which is 8 bytes on 64-bit,
but the buffer elements are only 4 bytes. The same function already
uses sizeof(*meas) on line 312, making the mismatch evident. Use
sizeof(*meas) consistently.

Fixes: b2e171f5a5c6 ("iio: sps30: add support for serial interface")
Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
Acked-by: Tomasz Duszynski <tduszyns@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>