staging: lustre: libcfs: nidstrings: Change type in printf format string

Wrong type in printf format string, requires 'unsigned int'
but the argument type is 'int'

This was found using a static code analysis program called cppcheck

Signed-off-by: Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>