process: fix compiler warning
process: fix compiler warning

../src/process.cpp: In member function ‘bool
xorg::testing::Process::WaitForExit(unsigned int)’:
../src/process.cpp:130:33: warning: comparison between signed and unsigned
integer expressions [-Wsign-compare]

Signed-off-by: Peter Hutterer <b9c50af7afa7642f6f854434cda9ffe54ece8b85@who-t.net>
Reviewed-by: Matt Dew <efc14b54fc305e4fa62231c5c6117533d0197c72@osource.org>
Reviewed-by: Chase Douglas <69e02ec421aa70a149511825d897f2549ceee9a2@canonical.com>

freedesktop-unofficial-mirror/xorg__test__xorg-gtest,freedesktop-unofficial-mirror/xorg__test__xorg-gtest,freedesktop-unofficial-mirror/xorg__test__xorg-gtest