staging: i4l: icn: use memdup_user

Its better to use memdup_user which does the same thing which this
code has implemented. Also removed a related warning as we will be
warned if allocation fails.

Suggested-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Sudip Mukherjee <sudip.mukherjee@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>