mfd: Remove redundant spi driver bus initialization

mfd: Remove redundant spi driver bus initialization

In ancient times it was necessary to manually initialize the bus field of an
spi_driver to spi_bus_type. These days this is done in spi_driver_register() so
we can drop the manual assignment.

The patch was generated using the following coccinelle semantic patch:
// <smpl>
@@
identifier _driver;
@@
struct spi_driver _driver = {
    .driver = {
-           .bus = &spi_bus_type,
    },
};
// </smpl>

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Cc: Srinidhi Kasagar <srinidhi.kasagar@stericsson.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>