mt76: mt7615: fix endianness in unified command

Fix cid field endianness in unified mt7615_uni_txd header

Reported-by: kbuild test robot <lkp@intel.com>
Fixes: 323d7daa ("mt76: mt7615: introduce uni cmd command types")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/2447b399d3c63885d43f65ba988c057fa96f5236.1584534454.git.lorenzo@kernel.org