brcmfmac: remove stale code from brcmf_sdcard_recv_chain()

The function brcmf_sdcard_recv_chain() has been reworked with
commit "brcmfmac: add sdio sg list support", but the incr_fix
variable is only assigned but not used so removing it now.

Reviewed-by: Franky Lin <frankyl@broadcom.com>
Reviewed-by: Hante Meuleman <meuleman@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>