brcmfmac: use strlcpy() instead of strcpy()

The function strcpy() is inherently not safe. Though the function
works without problems here, it would be better to use other safer
function, e.g. strlcpy(), to replace strcpy() still.

Signed-off-by: Neo Jou <neojou@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>