btrfs-progs: cleanup, update function definitions to be ANSI conformant

Sparse reports:

 warning: non-ANSI function declaration of function

and we're using func(void) elsewhere.

Signed-off-by: David Sterba <dsterba@suse.com>

btrfs-calc-size.c

@@ -421,7 +421,7 @@ out:
 	return ret;
 }
 
-static void usage()
+static void usage(void)
 {
 	fprintf(stderr, "Usage: calc-size [-v] [-b] <device>\n");
 }

qgroup.c

@@ -272,7 +272,7 @@ static void print_single_qgroup_table(struct btrfs_qgroup *qgroup)
 	printf("\n");
 }
 
-static void print_table_head()
+static void print_table_head(void)
 {
 	int i;
 	int len;

utils.c

@@ -2550,7 +2550,7 @@ int test_dev_for_mkfs(char *file, int force_overwrite)
 	return 0;
 }
 
-int btrfs_scan_lblkid()
+int btrfs_scan_lblkid(void)
 {
 	int fd = -1;
 	int ret;