ARM: dts: stm32: phyboard-sargas: Fix uart4 and sai2 pinctrl

ARM: dts: stm32: phyboard-sargas: Fix uart4 and sai2 pinctrl

- UART4:
  "uart4_pins_a" pinmux option does not apply here, as PB9 should be
  used for UART4_TX instead of PG11 (PG11 is LCD_B3 on Sargas).
  Use "uart4_pins_f" instead.
  Also remove "pinctrl-3" which is useless (identical to "pinctrl-1").

- SAI2 A:
  "sai2a_pins_b" pinmux option does not apply here, as only PI6 is used
  for SAI2 A ("SAI2_SD_A"). Other pins of this group (PI7 and PD13) are
  not used for audio.
  Use "sai2a_sleep_pins_d" instead.

Signed-off-by: Christophe Parant <c.parant@phytec.fr>
Link: https://lore.kernel.org/r/20251210101611.27008-6-c.parant@phytec.fr
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>