ARM: dts: stm32: Drop MMCI interrupt-names

The pl18x MMCI driver does not use the interrupt-names property,
the binding document has been updated to recommend this property
be unused, remove it.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Yann Gautier <yann.gautier@foss.st.com>
Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>