ftrace: Fix accounting bug with direct->count in register_ftrace_direct()

The direct->count wasn't being updated properly, where it only was updated
when the first entry was added, but should be updated every time.

Fixes: 013bf0da ("ftrace: Add ftrace_find_direct_func()")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>