ring-buffer: Simplify reset_disabled_cpu_buffer() with use of guard()

Use guard(raw_spinlock_irqsave)() in reset_disabled_cpu_buffer() to
simplify the locking.

Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/20250527144623.77a9cc47@gandalf.local.home


Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>