staging: unisys: uislib: uisutils.c: Fix a missing va_end

A missing va_end in connection with vsnprintf

Was found by 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>