ARM: dts: stm32: Fix SPI controller node names

SPI controller nodes should be named 'spi' rather than 'qspi'. Fixing the
name enables dtc SPI bus checks.

Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>