modsign: log module name in the event of an error

Now that we have the load_info struct all initialized (including
info->name, which contains the name of the module) before
module_sig_check(), make the load_info struct and hence module name
available to mod_verify_sig() so that we can log the module name in the
event of an error.

Signed-off-by: Jessica Yu <jeyu@kernel.org>