brcmfmac: Avoid build error with make W=1

When I run make W=1 on gcc (Debian 7.2.0-16) 7.2.0 I got an error for
the first run, all next ones are okay.

  CC [M]  drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.o
drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.c:2078: error: Cannot parse struct or union!
scripts/Makefile.build:310: recipe for target 'drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.o' failed

Seems like something happened with W=1 and wrong kernel doc format.
As a quick fix remove dubious /** in the code.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>