wifi: brcmfmac: fix scheduling while atomic issue when deleting flowring

We should not sleep while holding the spin lock. It makes
'scheduling while atomic' in brcmf_msgbuf_delete_flowring.
And to avoid race condition between deleting flowring and txflow,
we only hold spin lock when seting flowring status to RING_CLOSING.

Signed-off-by: Wright Feng <wright.feng@cypress.com>
Signed-off-by: Chi-Hsien Lin <chi-hsien.lin@cypress.com>
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220722115632.620681-3-alvin@pqrs.dk