It will not work, and the problem is not with dmidecode. Due to OS architectural differences you can't use that function of flashrom on OS X, it's a leftover from the Linux or BSD versions or whatever.
Flashrom is trying to have dmidecode read dmi data from /dev/mem which on Linux provides access to certain memory locations. On OS X there is no such thing, there is nothing there for dmidecode to read. You can't "fix" this.
Google "what is /dev/mem/" for more information.
Install Linux on your Mac, then it will work.
If you want to get at your DMI data then follow the instructions in the first post or follow the link I posted and use the other app.