Staging: iio: Fixed a punctuation and a spelling mistake.

Added a missing comma and changed 'it it useful' to 'it is useful'.
Signed-off-by: Ankit Baluni <b18007@students.iitmandi.ac.in>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/Documentation/overview.txt

@@ -9,7 +9,7 @@ The aim is to fill the gap between the somewhat similar hwmon and
 input subsystems.  Hwmon is very much directed at low sample rate
 sensors used in applications such as fan speed control and temperature
 measurement.  Input is, as its name suggests focused on input
-devices. In some cases there is considerable overlap between these and
+devices. In some cases, there is considerable overlap between these and
 IIO.
 
 A typical device falling into this category would be connected via SPI
@@ -38,7 +38,7 @@ series and Analog Devices ADXL345 accelerometers.  Each buffer supports
 polling to establish when data is available.
 
 * Trigger and software buffer support. In many data analysis
-applications it it useful to be able to capture data based on some
+applications it is useful to be able to capture data based on some
 external signal (trigger).  These triggers might be a data ready
 signal, a gpio line connected to some external system or an on
 processor periodic interrupt.  A single trigger may initialize data