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

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

arch/x86/net/bpf_jit_comp32.c

@@ -1847,7 +1847,7 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 			case BPF_B:
 			case BPF_H:
 			case BPF_W:
-				if (!bpf_prog->aux->verifier_zext)
+				if (bpf_prog->aux->verifier_zext)
 					break;
 				if (dstk) {
 					EMIT3(0xC7, add_1reg(0x40, IA32_EBP),