perf, powerpc: Use perf_sample_data_init() for the FSL code

We should use perf_sample_data_init() to initialize struct
perf_sample_data.  As explained in the description of commit dc1d628a
("perf: Provide generic perf_sample_data initialization"), it is
possible for userspace to get the kernel to dereference data.raw,
so if it is not initialized, that means that unprivileged userspace
can possibly oops the kernel.  Using perf_sample_data_init makes sure
it gets initialized to NULL.

This conversion should have been included in commit dc1d628a, but it
got missed.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Kumar Gala <kumar.gala@freescale.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>