staging: iio: adc: remove space after cast

Remove the space after an explicit cast because there is no
point in having it

Signed-off-by: Ioana Ciornei <ciorneiioana@gmail.com>
Reviewed-by: Daniel Baluta <daniel.baluta@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>