rasdaemon: Fix poll() on per_cpu trace_pipe_raw blocks indefinitely

rasdaemon: Fix poll() on per_cpu trace_pipe_raw blocks indefinitely

The error events are not received in the rasdaemon since kernel 6.1-rc6.
This issue is firstly detected and reported, when testing the CXL error
events in the rasdaemon.

Debugging showed, poll() on trace_pipe_raw in the ras-events.c do not
return and this issue is seen after the commit
42fb0a1e84ff525ebe560e2baf9451ab69127e2b ("tracing/ring-buffer: Have
polling block on watermark").

This issue is also verified using a test application for poll()
and select() on per_cpu trace_pipe_raw.

There is also a bug reported on this issue,
https://lore.kernel.org/all/31eb3b12-3350-90a4-a0d9-d1494db7cf74@oracle.com/

This issue occurs for the per_cpu case, which calls the ring_buffer_poll_wait(),
in kernel/trace/ring_buffer.c, with the buffer_percent > 0 and then wait until
the percentage of pages are available. The default value set for the
buffer_percent is 50 in the kernel/trace/trace.c. However poll() does not return
even met the percentage of pages condition.

As a fix, rasdaemon set buffer_percent as 0 through the
/sys/kernel/debug/tracing/instances/rasdaemon/buffer_percent, then the
task will wake up as soon as data is added to any of the specific cpu
buffer and poll() on per_cpu/cpuX/trace_pipe_raw does not block
indefinitely.

Dependency on the kernel fix commit
3e46d910d8acf94e5360126593b68bf4fee4c4a1("tracing: Fix poll() and select()
do not work on per_cpu trace_pipe and trace_pipe_raw")

Signed-off-by: Shiju Jose <shiju.jose@huawei.com>