support: fix typo in mkusers

This fixes the spurious "[: too many arguments" errors from mkusers.

Signed-off-by: Philip Paeps <philip@paeps.cx>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

support/scripts/mkusers

@@ -63,7 +63,7 @@ get_uid() {
 get_ugid() {
     local username="${1}"
 
-    awk -F:i -v username="${username}"                          \
+    awk -F: -v username="${username}"                          \
         '$1 == username { printf( "%d\n", $4 ); }' "${PASSWD}"
 }