wifi: ath12k: Remove some dead code

ATH12K_HE_MCS_MAX = 11, so this test and the following one are the same.
Remove the one with the hard coded 11 value.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/c17edf0811156a33bae6c5cf1906d751cc87edd4.1682423828.git.christophe.jaillet@wanadoo.fr