wifi: rt2x00: remove useless code in rt2x00queue_create_tx_descriptor()

In 'rt2x00queue_create_tx_descriptor()', there is no need to call
'ieee80211_get_rts_cts_rate()' while checking for RTS/CTS frame
since this function returns NULL or pointer to internal bitrate
table entry, and the return value is not actually used. Compile
tested only.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Acked-by: Stanislaw Gruszka <stf_xl@wp.pl>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/20231213051449.126963-1-dmantipov@yandex.ru