staging: rtl8192e: rename SeqNum to seq_num in sequence_control union

Fixes a checkpatch CHECK message.

Signed-off-by: William Durand <will+git@drnd.me>
Link: https://lore.kernel.org/r/20210214140332.16175-4-will+git@drnd.me


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