mkbootfs: Fix -f typo in usage message

Bug: 328362894
Change-Id: I559fb2640cb9fda7dbba172709ad1c3a7f3b6dd9
diff --git a/mkbootfs/mkbootfs.c b/mkbootfs/mkbootfs.c
index d3922bf..569a10c 100644
--- a/mkbootfs/mkbootfs.c
+++ b/mkbootfs/mkbootfs.c
@@ -402,7 +402,7 @@
 static void usage(void)
 {
     fprintf(stderr,
-            "Usage: mkbootfs [-n FILE] [-d DIR|-F FILE] DIR...\n"
+            "Usage: mkbootfs [-n FILE] [-d DIR|-f FILE] DIR...\n"
             "\n"
             "\t-d, --dirname=DIR: fs-config directory\n"
             "\t-f, --file=FILE: Canned configuration file\n"