cmd: host: Mandate the filename parameter in the 'bind' command

At present the host bind command does not require filename to be
provided. When it is not given NULL is passed to the host device
driver, which ends up failure afterwards.

Change to mandate the filename so that it is useful.

Signed-off-by: Bin Meng <bmeng@tinylab.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/host.c b/cmd/host.c
index fb1cb1f..b924940 100644
--- a/cmd/host.c
+++ b/cmd/host.c
@@ -59,10 +59,10 @@
 		argv++;
 	}
 
-	if (argc > 2)
+	if (argc != 2)
 		return CMD_RET_USAGE;
 	label = argv[0];
-	file = argc > 1 ? argv[1] : NULL;
+	file = argv[1];
 
 	ret = host_create_attach_file(label, file, removable, &dev);
 	if (ret) {
@@ -253,7 +253,7 @@
 	"host save hostfs - <addr> <filename> <bytes> [<offset>] - "
 		"save a file to host\n"
 	"host size hostfs - <filename> - determine size of file on host\n"
-	"host bind [-r] <label> [<filename>] - bind \"host\" device to file\n"
+	"host bind [-r] <label> <filename> - bind \"host\" device to file\n"
 	"     -r = mark as removable\n"
 	"host unbind <label>     - unbind file from \"host\" device\n"
 	"host info [<label>]     - show device binding & info\n"