build.sh: print usage when no argument is passed

Without it, the script failed with cryptic error:

    $ ./build.sh
    ./build.sh: line 259: $1: unbound variable

Change-Id: I2472c3451d6754f978f39b23a3492ed369151861
Signed-off-by: Krystian Hebel <[email protected]>

Author: krystian-hebel

build.sh

@@ -256,6 +256,11 @@ function build_odroid_h4 {
   fi
 }
 
+if [ $# -lt 1 ]; then
+  usage
+  exit
+fi
+
 CMD="$1"
 
 case "$CMD" in