x86/cpu/vmware: Do not trace vmware_sched_clock()

When running function tracing on a Linux guest running on VMware
Workstation, the guest would crash. This is due to tracing of the
sched_clock internal call of the VMware vmware_sched_clock(), which
causes an infinite recursion within the tracing code (clock calls must
not be traced).

Make vmware_sched_clock() not traced by ftrace.

Fixes: 80e9a4f2 ("x86/vmware: Add paravirt sched clock")
Reported-by: GwanYeong Kim <gy741.kim@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
CC: Alok Kataria <akataria@vmware.com>
CC: GwanYeong Kim <gy741.kim@gmail.com>
CC: "H. Peter Anvin" <hpa@zytor.com>
CC: Ingo Molnar <mingo@kernel.org>
Cc: stable@vger.kernel.org
CC: Thomas Gleixner <tglx@linutronix.de>
CC: virtualization@lists.linux-foundation.org
CC: x86-ml <x86@kernel.org>
Link: http://lkml.kernel.org/r/20181109152207.4d3e7d70@gandalf.local.home