mmc: core: Remove dead code

bus_width is passed to the function and when 0 (MMC_BUS_WIDTH_1)
will cause the function to return. So in in the second test it
definitely is different from 0, and the third test is redundant.

Signed-off-by: Philippe De Swert <philippedeswert@gmail.com>
Reviewed-by: Namjae Jeon <linkinjeon@gmail.com>
Acked-by: Philip Rakity <prakity@marvell.com>
Signed-off-by: Chris Ball <cjb@laptop.org>