staging: r8188eu: simplify the checks for zero address

In function ap2sta_data_frame, we can use is_zero_ether_addr to check for
all-zero ethernet addresses. Both pattrib->bssid and mybssid are 16-bit
aligned.

Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20221126154253.178275-5-martin@kaiser.cx


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>