dts/arm/st: fix dts inclusion for stm32f334

stm32f334 is not an expansion of stm32f303, since
stm32f303 has more I2C, SPI ports than stm32f303.

Fix this by including stm32f3.dtsi in stm32f334.dtsi.

Signed-off-by: Yannis Damigos <giannis.damigos@gmail.com>