mount_root: fix compilation error for wrong condition

mount_root: fix compilation error for wrong condition

While reworking this to new implementation, a broken and old commit
slipped in by mistake.

Fix compilation error for wrong condition.

mount_root.c: In function 'main':
mount_root.c:131:23: error: expected expression before '||' token
  131 |         if (argc < 2) || (!strcmp(argv[1], "start"))
      |                       ^~
mount_root.c: At top level:
mount_root.c:31:1: error: 'start' defined but not used [-Werror=unused-function]
   31 | start(int argc, char *argv[3])
      | ^~~~~
cc1: all warnings being treated as errors

Fixes: 1a5695925ecf ("mount_root: add support for passing args to mount_root start")
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>