brcmfmac: Remove duplicate struct declaration

struct brcmf_bus is declared twice. One has been declared
at 37th line. Remove the duplicate.

Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210331023557.2804128-2-wanjiabing@vivo.com