platform/x86: asus-wmi: Potential buffer overflow in asus_wmi_evaluate_method_buf()

This code tests for if the obj->buffer.length is larger than the buffer
but then it just does the memcpy() anyway.

Fixes: 0f0ac158

 ("platform/x86: asus-wmi: Add support for custom fan curves")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20220413073744.GB8812@kili
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>