[EMULATORS] net: Fix smc91c111_emulator_read()

The statement "*(u32 *)dst = 0x0;" in smc91c111_emulator_read() is
a bug because it will corrupt memory when dst_len = 1 or 2 hence
this patch fixes this bug.

Reported-by: Po-wen Cheng <sting.cheng@gmail.com>
Signed-off-by: Anup Patel <anup@brainfault.org>