VPP-189 Fix coverity warnings
VPP-189 Fix coverity warnings

in api_format.c.

Change-Id: Iedc510fe962b6e8fb8614be4038e695b13e12ef9
Signed-off-by: Dave Barach <bfcdf3e6ca6cef45543bfbb57509c92aec9a39fb@barachs.net>

chrisy/vpp,vpp-dev/vpp,vpp-dev/vpp,GabrielGanne/vpp-flowtable,FDio/vpp,chrisy/vpp,GabrielGanne/vpp-flowtable,milanlenco/vpp,FDio/vpp,milanlenco/vpp,FDio/vpp,FDio/vpp,GabrielGanne/vpp-flowtable,FDio/vpp,FDio/vpp,vpp-dev/vpp,vpp-dev/vpp,GabrielGanne/vpp-flowtable,chrisy/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,GabrielGanne/vpp-flowtable,milanlenco/vpp,chrisy/vpp,vpp-dev/vpp,GabrielGanne/vpp-flowtable,milanlenco/vpp,vpp-dev/vpp,milanlenco/vpp,FDio/vpp,chrisy/vpp,vpp-dev/vpp,milanlenco/vpp,chrisy/vpp