spi: spi-cadence-quadspi: Populate get_name() interface

Implement get_name() interface of spi_controller_mem_ops so as to avoid
changing of mtd->name due to driver being moved over to spi-mem
framework from SPI NOR. This avoids breaking of MTD cmdline args being
passed by bootloaders which maybe using old driver name.

Fixes: 31fb632b

 ("spi: Move cadence-quadspi driver to drivers/spi/")
Reported-by: Jan Kiszka <jan.kiszka@siemens.com>
Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20200825172506.14375-1-vigneshr@ti.com
Signed-off-by: Mark Brown <broonie@kernel.org>