bpf, x86_32: Fix logic error in BPF_LDX zero-extension

commit 5ca1ca01 upstream.

When verifier_zext is true, we don't need to emit code
for zero-extension.

Fixes: 836256bf ("x32: bpf: eliminate zero extension code-gen")
Signed-off-by: Wang YanQing <udknight@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200423050637.GA4029@udknight


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>