printf: incorrect exit code when passing invalid value to `%x`

With GNU:
```
/usr/bin/printf %x %194 > /dev/null
echo $?
```
returns:
```
/usr/bin/printf: '%194': expected a numeric value
1
```
With our Rust implementation:
```
./target/debug/coreutils printf %x %194 > /dev/null
echo $? 
```
returns:
```
printf: '%194': value not completely converted
0
```