checkpatch.pl: fix CAST detection

We should only claim that something is a cast if we did not encouter a
token before, that did set av_pending.

This fixes the operator * in the line below to be detected as binary (vs
unary).

kmalloc(sizeof(struct alphatrack_ocmd) * true_size, GFP_KERNEL);

Reported-by: Peter Chubb <nicta.com.au>
Signed-off-by: Florian Mickler <florian@mickler.org>
(cherry-picked from Linux kernel commit c023e4734c3e8801e0ecb5e81b831d42a374d861)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: Blue Swirl <blauwirbel@gmail.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
