m2mresource: make code great again after commit 5539d121da4
m2mresource: make code great again after commit 5539d121da4

Previous commit (5539d121da4) broke the build, fix this.

tridonic-com/mbed-client,ARMmbed/mbed-client,tridonic-com/mbed-client,tridonic-com/mbed-client,ARMmbed/mbed-client,ARMmbed/mbed-client