sfc: Fix spelling mistake "writting" -> "writing"

There are some spelling mistakes in the comment. Fix it.

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Lv Ruyi <lv.ruyi@zte.com.cn>
Link: https://lore.kernel.org/r/20220411032546.2517628-1-lv.ruyi@zte.com.cn


Signed-off-by: Paolo Abeni <pabeni@redhat.com>