The renaming of "master" to "controller" done in
    812a9dd
    spi: Generalize SPI "master" to "controller"

breaks the spi command, because the spi.master pointer is not assigned.
The pointer is kept for backwards compatability.

Assign it, so that spi drivers that are still using "spi->master" can be
used.

Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>