ARM: dts: stm32: use uniform label names for sleep pinctrl phandles

Some labels follow the *_sleep_pins_* naming scheme, but some also use
*_pins_sleep_*. Because most labels use the former and for uniformity
with variants like sdmmc1_b4_pins_a and sdmmc1_dir_pins_a, adopt the
*_sleep_pins_* scheme throughout.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>