vmctl: use a space rather than tab in usage

[David Demelier]

Most utilities seem to use a unique space between the colon and the
program name, vmctl uses a tab that will expand to two spaces once
invoked.

e.g.

pfctl: unknown command line argument: tata ...
usage: pfctl [-deghNnPqrvz] [-a anchor] [-D macro=value] [-F modifier]
[-f file]

tar foobar
tar: f argument missing
usage: tar {crtux}[014578befHhjLmNOoPpqsvwXZz]

vmctl oops
unknown argument: oops
usage:  vmctl [-v] command [arg ...]

The style(9) manual page seems to recommend a unique space though:

     The getprogname(3) function may be used instead of hard-coding the
     program name.

           fprintf(stderr, "usage: %s [-ab]\n", getprogname());
           exit(1);

Index: main.c
===================================================================
RCS file: /cvs/src/usr.sbin/vmctl/main.c,v
retrieving revision 1.73
diff -u -p -u -p -r1.73 main.c
--- main.c      1 Sep 2022 15:43:07 -0000       1.73
+++ main.c      30 Dec 2022 13:39:37 -0000
@@ -96,7 +96,7 @@ usage(void)
 {
        extern char     *__progname;
 
-       fprintf(stderr, "usage:\t%s [-v] command [arg ...]\n",
__progname);
+       fprintf(stderr, "usage: %s [-v] command [arg ...]\n",
__progname);
 
        exit(1);
 }
@@ -106,7 +106,7 @@ ctl_usage(struct ctl_command *ctl)
 {
        extern char     *__progname;
 
-       fprintf(stderr, "usage:\t%s [-v] %s %s\n", __progname,
+       fprintf(stderr, "usage: %s [-v] %s %s\n", __progname,
            ctl->name, ctl->usage);
        exit(1);
 }