ARM: dts: armada388-clearfog: fix SPI flash #size-cells

The SPI flash #size-cells is specified in the binding documentation to
have value 1, but we were setting it to zero.  This wasn't causing any
problem as we do not list any partitions, but it's worth specifying
correctly if we're going to specify it at all.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>