tracing: Fix ring-buffer and ksym tracer merge interaction

The compiler warns us about:

  kernel/trace/trace_ksym.c: In function ksym_hbp_handler:
  kernel/trace/trace_ksym.c:92: attention : passing argument 1 of trace_buffer_lock_reserve from incompatible pointer type
  kernel/trace/trace_ksym.c:106: attention : passing argument 1 of trace_buffer_unlock_commit from incompatible pointer type

Commit "e77405ad" (tracing: pass around ring buffer
instead of tracer) has changed the central tracing
APIs. And this change has updated every callsites of
these APIs except those that aren't in tracing/core,
such as the ksym tracer.

Cc: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>