esp32/README: Fix board in octal-SPIRAM example make command.

Signed-off-by: eggfly <[email protected]>

Author: eggfly

ports/esp32/README.md

@@ -152,7 +152,7 @@ $ make BOARD=ESP32_GENERIC BOARD_VARIANT=OTA
 or to enable octal-SPIRAM support for the `ESP32_GENERIC_S3` board:
 
 ```bash
-$ make BOARD=ESP32_GENERIC BOARD_VARIANT=SPIRAM_OCT
+$ make BOARD=ESP32_GENERIC_S3 BOARD_VARIANT=SPIRAM_OCT
 ```