staging: wfx: simplify wfx_flush()

Current code of wfx_flush() force to drop packets in some contexts.
However, there is no obvious reasons to do that. It looks like a
workaround for a bug with the old implementation of __wfx_flush().

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200115135338.14374-21-Jerome.Pouiller@silabs.com


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