blackfin: mmc: Correct mmc_host_is_spi and bfin_sdh.c

In the recent mmc cleanup, the mmc_host_is_spi macro was broken and
bfin_sdh.c had mmc->bus_width turned into mmc_bus_width(mmc), both of
which were incorrect.

Signed-off-by: Tom Rini <trini@ti.com>