rpi-eeprom: Add SIGN_API compile dependency

Make sure to rebuild the firmware for signed images and not just re-use
the cached copy.

Change-type: patch
Signed-off-by: Alex Gonzalez <alexg@balena.io>

layers/meta-balena-raspberrypi/recipes-bsp/rpi-eeprom/rpi-eeprom_git.bb

@@ -97,6 +97,7 @@ do_compile[depends] += " \
     python3-pycryptodomex-native:do_populate_sysroot \
     balena-keys:do_deploy \
 "
+do_compile[vardeps] = "SIGN_API"
 
 do_install() {
   install -d ${D}${libexecdir}