util/nvmutil: fix bad print specifier (c90)

size_t may be unsigned long long, but lu
is for unsigned long. the integer is small
enough that we don't need to worry, so let's
just cast it accordingly (inside err)

Signed-off-by: Leah Rowe <leah@libreboot.org>

util/nvmutil/nvmutil.c

@@ -534,7 +534,7 @@ sanitize_command_index(size_t c)
 
 	if (command[c].argc < 3)
 		err(ECANCELED, "cmd index %lu: argc below 3, %d",
-		    c, command[c].argc);
+		    (unsigned long)c, command[c].argc);
 
 	if (command[c].str == NULL)
 		err(ECANCELED, "cmd index %lu: NULL str", c);