mwifiex: drop redundant null-pointer check in mwifiex_dnld_cmd_to_fw()

There is no case in which the variable cmd_node->cmd_skb has no ->data,
and thus the variable host_cmd is guaranteed to be not NULL. Therefore,
the null-pointer check is redundant and can be dropped.

Reported-by: TOTE Robot <oslab@tsinghua.edu.cn>
Signed-off-by: Tuo Li <islituo@gmail.com>
Tested-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210804020305.29812-1-islituo@gmail.com