testdisplay: set a non-zero exit code if getopt detected an error
testdisplay: set a non-zero exit code if getopt detected an error

Signed-off-by: Thomas Wood <b9025d6a953b68f894a0f6a80fd2af6d55b0badd@intel.com>

chenxianqin/intel-gpu-tools,mv0/intel-gpu-tools,erikarn/intel-gpu-tools,dlespiau/checkmate-test-igt,yipdw/intel-gpu-tools,erikarn/intel-gpu-tools,erikarn/intel-gpu-tools,yipdw/intel-gpu-tools,tiagovignatti/intel-gpu-tools,chenxianqin/intel-gpu-tools,mv0/intel-gpu-tools,yipdw/intel-gpu-tools,dlespiau/checkmate-test-igt,tiagovignatti/intel-gpu-tools,erikarn/intel-gpu-tools,chenxianqin/intel-gpu-tools,tiagovignatti/intel-gpu-tools,mv0/intel-gpu-tools,chenxianqin/intel-gpu-tools,mv0/intel-gpu-tools,dlespiau/checkmate-test-igt,tiagovignatti/intel-gpu-tools,yipdw/intel-gpu-tools,dlespiau/checkmate-test-igt