dd: error message on count=KBb doesn't match GNU dd, but should

GNU dd:
```
$ : | dd count=KBb
dd: invalid number: ‘KBb’
```

uutils dd:
```
$ : | ./target/debug/dd count=KBb
./target/debug/dd: Unrecognized byte multiplier -> KB
```
This should be `invalid number: 'KBb'`, just like the GNU version of dd.


This is from the GNU test suite file `tests/dd/bytes.sh`.