brcmfmac: fix system warning message during wowl suspend

There is a system warning message, warn_slowpath-fmt, during suspend
while using supplicant join AP and enable wowl feature by IW command.
It's caused by brcmf_pno_remove_request path can't find the reqid.
This fix will not go to remove pno request function if there is no
pno scan.

Acked-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Lo-Hsiang Lo <double.lo@cypress.com>
Signed-off-by: Chi-Hsien Lin <chi-hsien.lin@cypress.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>