Macbook pro boot with kernel panic - can't perform kext scan
The safest thing to do is boot into OS X Recovery and re-install the OS.

You could alternatively boot into Recovery and open terminal and hope to fix the format of the kext file on disk, but I'd say it would be safer to start that Mac in target mode and copy in an unmodified copy of IOHIDFamily.kext into /System/Library/Extensions

Unless you have a good backup of the Mac, it's safer to just reinstall the core OS which will leave your user files and accounts alone, but remedy this system file that is needed for the system to run.