More LERDGE envs followup (#21205)

platformio.ini

 # Lerdge X with USB Flash Drive Support
 #
 [env:LERDGEX_usb_flash_drive]
-platform          = ${LERDGEX.platform}
+platform          = ${env:LERDGEX.platform}
 extends           = LERDGEX
 platform_packages = ${stm32_flash_drive.platform_packages}
 build_flags       = ${stm32_flash_drive.build_flags}
 # Lerdge S with USB Flash Drive Support
 #
 [env:LERDGES_usb_flash_drive]
-platform          = ${LERDGES.platform}
+platform          = ${env:LERDGES.platform}
 extends           = LERDGES
 platform_packages = ${stm32_flash_drive.platform_packages}
 build_flags       = ${stm32_flash_drive.build_flags}
 # Lerdge K with USB Flash Drive Support
 #
 [env:LERDGEK_usb_flash_drive]
-platform          = ${LERDGEK.platform}
+platform          = ${env:LERDGEK.platform}
 extends           = LERDGEK
 platform_packages = ${stm32_flash_drive.platform_packages}
 build_flags       = ${stm32_flash_drive.build_flags}