brcmfmac: fix bus interface selection in Kconfig

The kernel configuration for the driver could result in
compilation issues as reported by Randy Dunlap. His results
are show below:

"on x86_64:

when
CONFIG_MMC=m
CONFIG_BRCMUTIL=y
CONFIG_BRCMFMAC=y
CONFIG_BRCMFMAC_SDIO=y

This bool kconfig symbol:

config BRCMFMAC_SDIO
	bool "SDIO bus interface support for FullMAC driver"
	depends on MMC

allows BRCMFMAC_SDIO to be y even when MMC=m.

Is there a reasonable solution to this?

This causes many build errors:

drivers/built-in.o: In function `brcmf_sdio_assert_info':
dhd_sdio.c:(.text+0x39609b): undefined reference to `sdio_claim_host'
dhd_sdio.c:(.text+0x3960d9): undefined reference to `sdio_release_host'
drivers/built-in.o: In function `brcmf_sdio_readframes':
dhd_sdio.c:(.text+0x396a62): undefined reference to `sdio_claim_host'
dhd_sdio.c:(.text+0x396a9b): undefined reference to `sdio_release_host'
..."

This patch adds the appropriate logic in Kconfig to resolve
these issues. The solution was provided by Hauke Mehrtens.

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Hauke Mehrtens <hauke@hauke-m.de>
Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>