[WHY]
The memcpy() function copies n bytes from memory area src to memory area
dest. So specify the firmware size in bytes.

[How]
Correct the calculation.
Acked-by: NEvan Quan <evan.quan@amd.com>
Signed-off-by: Lei Guo <raykwok1150@163.com>
Reviewed-by: NJunwei Zhang <zjunweihit@163.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>