Corrected signed/unsigned integer comparison warnings.

Corrected signed/unsigned integer comparison warnings.

The return value of the ftell() function was assigned to an unsigned
integer typed variable and then compared to -1.  Since ftell() actually
returns a 'long' assign to a 'long' instead.  This addresses
signed/unsigned integer comparison warnings.

Change-Id: I990e891ee2ad1f81cd0721ad82646fcf2e79d2b0
Signed-off-by: Ossama Othman <ossama.othman@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/4689
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Jon A. Cruz <jonc@osg.samsung.com>