KVM: arm64: Remove potential UB on nvhe tracing clock update

KVM: arm64: Remove potential UB on nvhe tracing clock update

Sashiko(locally) reports possiblity of division by zero and
out-of-bounds bitwise shift in trace_clock_update().

Although the clock update is untrusted, we should at least have some
basic checks to avoid undefined behaviours.

Reviewed-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Mostafa Saleh <smostafa@google.com>
Link: https://patch.msgid.link/20260430103724.2151625-1-smostafa@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>