staging: iio: Use kcalloc instead of kzalloc

This patch uses kcalloc instead of kzalloc function.
A coccinelle script was used to make this change.

Signed-off-by: Navya Sri Nizamkari <navyasri.tech@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>