gcc-plugins: fix sancov_plugin for gcc-5

The name of the local variable was inadvertantly changed from
sancov_plugin_pass_info to sancov_pass_info:

scripts/gcc-plugins/sancov_plugin.c: In function ‘int plugin_init(plugin_name_args*, plugin_gcc_version*)’:
scripts/gcc-plugins/sancov_plugin.c:136:67: error: ‘sancov_plugin_pass_info’ was not declared in this scope

This changes the conditional reference to this variable as well.

Fixes: 5a45a4c5

 ("gcc-plugins: consolidate on PASS_INFO macro")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kees Cook <keescook@chromium.org>