riscv: dts: sifive unmatched: Link the tmp451 with its power supply

Fixes the following probe warning:
  lm90 0-004c: Looking up vcc-supply from device tree
  lm90 0-004c: Looking up vcc-supply property in node /soc/i2c@10030000/temperature-sensor@4c failed
  lm90 0-004c: supply vcc not found, using dummy regulator

Signed-off-by: Vincent Pelletier <plr.vincent@gmail.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>