COMP: Make sscanf format & variable match types

Addresses this issue:
https://issues.itk.org/jira/browse/ITK-3217

One of those gcc-only printf format check warnings.

Change-Id: If7f27745dc7fed0e3d1fe5c59fde685b38790d52
Merge topic 'FEMCompilerWarnings-3217'

e93f5ec COMP: Make sscanf format & variable match types