[Docs] Clarify how to use the bootloader LED for rp2040 (#18585)

docs/platformdev_rp2040.md

@@ -58,7 +58,7 @@ The double-tap reset mechanism is an alternate way in QMK to enter the embedded
 ```c
 #define RP2040_BOOTLOADER_DOUBLE_TAP_RESET // Activates the double-tap behavior
 #define RP2040_BOOTLOADER_DOUBLE_TAP_RESET_TIMEOUT 200U // Timeout window in ms in which the double tap can occur.
-#define RP2040_BOOTLOADER_DOUBLE_TAP_RESET_LED_MASK 0U // Specify a optional status led which blinks when entering the bootloader
+#define RP2040_BOOTLOADER_DOUBLE_TAP_RESET_LED GP17 // Specify a optional status led by GPIO number which blinks when entering the bootloader
 ```
 
 ## Pre-defined RP2040 boards