bios_emulator: Fix buffer overflow

bios_emulator: Fix buffer overflow

Using strcpy to copy a 4 character string into a 4 byte field in a
structure will overflow that field as it writes the terminating \0 into
the following field. Correct this by using memcpy instead.

This issue was found by Smatch.

Signed-off-by: Andrew Goodbody <andrew.goodbody@linaro.org>