examples/asymcute_mqttsn: fix target name
examples/asymcute_mqttsn: fix target name

Target name is `mosquitto_rsmb` and not `rsmb`.

cladmi/RIOT,mtausig/RIOT,A-Paul/RIOT,avmelnikoff/RIOT,avmelnikoff/RIOT,authmillenon/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,ant9000/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,rfuentess/RIOT,jasonatran/RIOT,jasonatran/RIOT,x3ro/RIOT,mtausig/RIOT,miri64/RIOT,smlng/RIOT,gebart/RIOT,BytesGalore/RIOT,biboc/RIOT,mtausig/RIOT,yogo1212/RIOT,yogo1212/RIOT,kbumsik/RIOT,biboc/RIOT,mfrey/RIOT,mfrey/RIOT,avmelnikoff/RIOT,biboc/RIOT,lazytech-org/RIOT,rfuentess/RIOT,OlegHahm/RIOT,aeneby/RIOT,kbumsik/RIOT,mfrey/RIOT,x3ro/RIOT,mfrey/RIOT,authmillenon/RIOT,BytesGalore/RIOT,x3ro/RIOT,basilfx/RIOT,lazytech-org/RIOT,kaspar030/RIOT,miri64/RIOT,aeneby/RIOT,OlegHahm/RIOT,A-Paul/RIOT,lazytech-org/RIOT,cladmi/RIOT,x3ro/RIOT,BytesGalore/RIOT,A-Paul/RIOT,mfrey/RIOT,BytesGalore/RIOT,basilfx/RIOT,A-Paul/RIOT,jasonatran/RIOT,yogo1212/RIOT,authmillenon/RIOT,OTAkeys/RIOT,authmillenon/RIOT,yogo1212/RIOT,authmillenon/RIOT,biboc/RIOT,basilfx/RIOT,kaspar030/RIOT,avmelnikoff/RIOT,avmelnikoff/RIOT,ant9000/RIOT,rfuentess/RIOT,kbumsik/RIOT,josephnoir/RIOT,ant9000/RIOT,cladmi/RIOT,OlegHahm/RIOT,lazytech-org/RIOT,kYc0o/RIOT,authmillenon/RIOT,jasonatran/RIOT,cladmi/RIOT,kaspar030/RIOT,toonst/RIOT,josephnoir/RIOT,A-Paul/RIOT,mtausig/RIOT,kYc0o/RIOT,BytesGalore/RIOT,smlng/RIOT,mtausig/RIOT,aeneby/RIOT,biboc/RIOT,rfuentess/RIOT,yogo1212/RIOT,OlegHahm/RIOT,gebart/RIOT,kaspar030/RIOT,OTAkeys/RIOT,kbumsik/RIOT,gebart/RIOT,basilfx/RIOT,toonst/RIOT,ant9000/RIOT,toonst/RIOT,gebart/RIOT,cladmi/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,kbumsik/RIOT,miri64/RIOT,miri64/RIOT,smlng/RIOT,aeneby/RIOT,x3ro/RIOT,smlng/RIOT,aeneby/RIOT,toonst/RIOT,kYc0o/RIOT,smlng/RIOT,yogo1212/RIOT,toonst/RIOT,kYc0o/RIOT,josephnoir/RIOT,lazytech-org/RIOT,jasonatran/RIOT,miri64/RIOT,gebart/RIOT,basilfx/RIOT,OTAkeys/RIOT,kaspar030/RIOT,josephnoir/RIOT,OlegHahm/RIOT,rfuentess/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,ant9000/RIOT,josephnoir/RIOT