edbg.inc.mk: handle IMAGE_OFFSET being defined with a space
edbg.inc.mk: handle IMAGE_OFFSET being defined with a space

Handle that `IMAGE_OFFSET` can be set to something that contain spaces.

With 'IMAGE_OFFSET=$$((0x1000 + 0x1000))' we had in the command line when doing
'flash'

    --offset $((0x1000 --offset + --offset 0x1000))

With the change we correctly have

    --offset $((0x1000 + 0x1000))

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