ARM: dts: da850-evm: fix read access to SPI flash

Read access to the SPI flash are broken on da850-evm, i.e. the data
read is not what is actually programmed on the flash.
According to the datasheet for the M25P64 part present on the da850-evm,
if the SPI frequency is higher than 20MHz then the READ command is not
usable anymore and only the FAST_READ command can be used to read data.

This commit specifies in the DTS that we should use FAST_READ command
instead of the READ command.

Cc: stable@vger.kernel.org
Tested-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Fabien Parent <fparent@baylibre.com>
[nsekhar@ti.com: subject line adjustment]
Signed-off-by: Sekhar Nori <nsekhar@ti.com>

Signed-off-by: Olof Johansson <olof@lixom.net>