ring_buffer: Change some static functions to bool

ring_buffer: Change some static functions to bool

The return values of some functions are of boolean type. Change the
type of these function to bool and adjust their return values. Also
change type of some internal varibles to bool.

No functional change intended.

Link: https://lkml.kernel.org/r/20230305155532.5549-3-ubizjak@gmail.com
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Reviewed-by: Mukesh Ojha <quic_mojha@quicinc.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>