mtd: devices: m25p80: Use spi_mem_set_drvdata() instead of spi_set_drvdata()

SPI mem drivers should use spi_mem_set_drvdata() not spi_set_drvdata()
to store their private data. Using spi_set_drvdata() will mess the
spi -> spi-mem link up and cause a kernel panic at shutdown or
device removal time.

Fixes: 4120f8d1 ("mtd: spi-nor: Use the spi_mem_xx() API")
Reported-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Marek Vasut <marek.vasut+renesas@gmail.com> on R8A7791 Porter
Signed-off-by: Mark Brown <broonie@kernel.org>