ec: Fix 32 bits issues on file size calculation

Some additional 32 bits issues have been added by a recent patch.
This patch solves it.

This is a backport of http://review.gluster.org/8882/

Change-Id: Ice81032fbe8e36e5ccad19a781b7876891993906
BUG: 1146904
Signed-off-by: Xavier Hernandez <xhernandez@datalab.es>
Reviewed-on: http://review.gluster.org/8883
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Dan Lambright <dlambrig@redhat.com>