system_info: Fix coding style warnings.

./system_info/system_info_instance.cc:90:  Missing spaces around =  [whitespace/operators] [4]
./system_info/system_info_instance.cc:111:  Missing spaces around =  [whitespace/operators] [4]
./system_info/system_info_instance.cc:120:  Missing spaces around =  [whitespace/operators] [4]