Change the return value of kvm_read/kvm_write to be -1 on error, to match the documented interface.
Change the return value of kvm_read/kvm_write to be -1 on error, to
match the documented interface.

Previously it returned 0 on error.

PR:		bin/10511

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase