module: fix ddebug_remove_module()

ddebug_remove_module() use mod->name to find the ddebug_table of the
module and remove it. But dynamic_debug_setup() use the first
_ddebug->modname to create ddebug_table for the module. It's ok when
the _ddebug->modname is the same with the mod->name.

But livepatch module is special, it may contain _ddebugs of other
modules, the modname of which is different from the name of livepatch
module. So ddebug_remove_module() can't use mod->name to find the
right ddebug_table and remove it. It can cause kernel crash when we cat
the file <debugfs>/dynamic_debug/control.

Signed-off-by: Zhou Chengming <zhouchengming1@huawei.com>
Signed-off-by: Jessica Yu <jeyu@kernel.org>