tracing: Use this_cpu_ptr per-cpu helper

tracing: Use this_cpu_ptr per-cpu helper

typeof(&buffer) is a pointer to array of 1024 char, or char (*)[1024].
But, typeof(&buffer[0]) is a pointer to char which match the return type of get_trace_buf().
As well-known, the value of &buffer is equal to &buffer[0].
so return this_cpu_ptr(&percpu_buffer->buffer[0]) can avoid type cast.

Link: http://lkml.kernel.org/r/[email protected]
Reviewed-by: Christoph Lameter <[email protected]>
Signed-off-by: Shan Wei <[email protected]>
Signed-off-by: Steven Rostedt <[email protected]>