As of now all filenames known by UBIFS are strings with a NUL
terminator. With encrypted filenames a filename can be any binary
string and the r5 function cannot search for the NUL terminator.
UBIFS always knows how long a filename is, therefore we can change
the hash function to iterate over the filename length to work
correctly with binary strings.
Signed-off-by: Richard Weinberger <richard@nod.at>