staging: wfx: fix comment correctness

Using DMA with stack allocated buffers is not supported, whatever the
value of CONFIG_VMAP_STACK.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20220113085524.1110708-5-Jerome.Pouiller@silabs.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>