Simplify footprint.sh

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/scripts/footprint.sh b/scripts/footprint.sh
index c228a26..1f29451 100755
--- a/scripts/footprint.sh
+++ b/scripts/footprint.sh
@@ -21,14 +21,14 @@
 CONFIG_H='include/mbedtls/mbedtls_config.h'
 CRYPTO_CONFIG_H='tf-psa-crypto/include/psa/crypto_config.h'
 
-if [ -r $CONFIG_H ]; then :; else
+if [ ! -r $CONFIG_H ]; then
     echo "$CONFIG_H not found" >&2
     echo "This script needs to be run from the root of" >&2
     echo "a git checkout or uncompressed tarball" >&2
     exit 1
 fi
 
-if [ -r $CRYPTO_CONFIG_H ]; then :; else
+if [ ! -r $CRYPTO_CONFIG_H ]; then
     echo "$CRYPTO_CONFIG_H not found" >&2
     echo "This script needs to be run from the root of" >&2
     echo "a git checkout or uncompressed tarball" >&2