brcmfmac: remove unnecessary EXPORT_SYMBOL() usage

In bcmsdh.c the functions brcmf_sdio_probe() and brcmf_sdio_remove()
were exported, but that is not needed. The functions are linked into
the driver module, which is the only one needing to call these.

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>