brcmfmac: do not load firmware when device is already running

In brcmf_usb_probe_cb() the device is checked to determine whether
it is already running firmware. However, when no firmware download
is needed it still continues to request the firmware files. This
is fixed by returning after successful setup.

Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Reviewed-by: Daniel (Deognyoun) Kim <dekim@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>