brcmfmac: initialize escan function pointer during scheduled scan

brcmfmac: initialize escan function pointer during scheduled scan

For scheduled scan results the driver does a escan to obtain BSS
details from the firmware. However, the escan uses a dynamically
determined function. This needs to be set appropriately when handling
scheduled scan results to avoid NULL pointer access.

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