Fix some gcc warnings

Fix some gcc warnings

These are:
"enumeral and non-enumeral type in conditional expression",
"comparison of unsigned expression >= 0 is always true",
and "address requested for 't', which is declared 'register'"

Change-Id: Ia9bab2e1e2c212a2889197e8dd5f7295dda9dadd
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Bradley T. Hughes <bradley.hughes@nokia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>