staging: iio: Fix typo in iio

Correct spelling typo in staging/iio

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Acked-by: Michael <Hennerich&lt;michael.hennerich@analog.com>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>