ftrace: Rename dup_hash() and comment it

ftrace: Rename dup_hash() and comment it

The name "dup_hash()" is a misnomer as it does not duplicate the hash that
is passed in, but instead moves its entities from that hash to a newly
allocated one. Rename it to "__move_hash()" (using starting underscores as
it is an internal function), and add some comments about what it does.

Link: https://lore.kernel.org/linux-trace-kernel/20240605180408.537723591@goodmis.org
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>