samples: usb: Exclude frdm_mcxc242 platform from dfu sample

frdm_mcxc242 does not support MCUboot. Exclude the platform from dfu
sample.

Signed-off-by: Michal Smola <[email protected]>

Author: michal-smola

samples/subsys/usb/dfu/sample.yaml

@@ -18,6 +18,7 @@ common:
     - teensy41
     - b_u585i_iot02a
     - frdm_kl25z
+    - frdm_mcxc242
     - lpcxpresso55s69/lpc55s69/cpu0
     - stm32l562e_dk/stm32l562xx/ns
   depends_on: usb_device