rsi: remove unnecessary check for 802.11 management packet

The function rsi_mgmt_pkt_to_core() is for passing the 802.11
management frames to mac80211. So, it is unnecessary to check
again for the frame type 802.11 management in this function.
It can be checked before passing to this function.

Signed-off-by: Prameela Rani Garnepudi <prameela.j04cs@gmail.com>
Signed-off-by: Amitkumar Karwar <amit.karwar@redpinesignals.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>