kaleidoscope-builder: When doing virtual builds, always clear COMPILER_PREFIX

When doing virtual builds, we never want to use the arch prefix. We want to use
the compiler as set.

Signed-off-by: Gergely Nagy <algernon@keyboard.io>

etc/kaleidoscope-builder.conf

@@ -24,8 +24,9 @@ if [ "${ARCH}" = "virtual" ]; then
     #
     if [ -z "${COMPILER_PATH}" ]; then
        COMPILER_PATH="/usr/bin/"
-       COMPILER_PREFIX=""
     fi
+
+    COMPILER_PREFIX=""
 else
    ARCH="avr"
 fi