rtl8187: Fix warning generated when strncpy() destination length matches the sixe argument

In gcc8, when the 3rd argument (size) of a call to strncpy() matches the
length of the first argument, the compiler warns of the possibility of an
unterminated string. Using strlcpy() forces a null at the end.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>