ARM: dts: stm32: Rename spi-flash/mx66l51235l@N to flash@N on DHCOM SoM

ARM: dts: stm32: Rename spi-flash/mx66l51235l@N to flash@N on DHCOM SoM

Fix the following dtbs_check warning:
spi-flash@0: $nodename:0: 'spi-flash@0' does not match '^flash(@.*)?$'

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
Cc: Patrice Chotard <patrice.chotard@foss.st.com>
Cc: Patrick Delaunay <patrick.delaunay@foss.st.com>
Cc: kernel@dh-electronics.com
Cc: linux-stm32@st-md-mailman.stormreply.com
To: linux-arm-kernel@lists.infradead.org
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>