brcmfmac: reduce log level for invalid scheduled scan request

When a regular scan does not return any networks user-space does
request a scheduled scan without any matchset or ssid. This can
not be handled by the firmware so we return -EINVAL. However, as
this request is done let us not add an error message to the log.

Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Reviewed-by: Daniel (Deognyoun) Kim <dekim@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>