tracing: Fix comment about prefix in arch_syscall_match_sym_name()

ppc64 has its own syscall prefix like ".SyS" or ".sys". Make the
comment in arch_syscall_match_sym_name() more understandable.

Link: http://lkml.kernel.org/r/513D842F.40205@huawei.com



Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@huawei.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>