MAINTAINERS: fix path for xtensa/riscv esp32 soc

The correct paths are soc/xtensa/espressif_esp32
and soc/riscv/espressif_esp32, not soc/xtensa/esp32
and soc/riscv/esp32.

Signed-off-by: Bartosz Bilas <bartosz.bilas@hotmail.com>