brcmfmac: get rid of brcmf_cfg80211_escan() function

The function brcmf_cfg80211_escan() is only called by brcmf_cfg80211_scan()
so there is no reason to split in two function especially since the latter
does not do an awful lot.

Reviewed-by: Hante Meuleman <hante.meuleman@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieter-paul.giesberts@broadcom.com>
Reviewed-by: Franky Lin <franky.lin@broadcom.com>
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>