ath11k: Fix an error handling path

ath11k: Fix an error handling path

[ Upstream commit e7bcc145bcd035e56da7b97b033c463b32a5ff80 ]

If 'kzalloc' fails, we must return an error code.

While at it, remove a useless initialization of 'err' which could hide the
issue.

Fixes: d5c65159f289 ("ath11k: driver for Qualcomm IEEE 802.11ax devices")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201122173943.1366167-1-christophe.jaillet@wanadoo.fr
Signed-off-by: Sasha Levin <sashal@kernel.org>