brcmfmac: Use consistent naming for bsscfgidx.

brcmfmac: Use consistent naming for bsscfgidx.

The variable bsscfgidx is used in different places with different
names, e.g. bsscfg, bssidx, bsscfg_idx. This patch cleans this up
by using bsscfgidx everywhere.

Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>