brcmfmac: Avoid GFP_ATOMIC when GFP_KERNEL is enough

A workqueue is not atomic, so constraints can be relaxed here.
GFP_KERNEL can be used instead of GFP_ATOMIC.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/b6e619415db4ee5de95389280d7195bb56e45f77.1618860716.git.christophe.jaillet@wanadoo.fr