dim: actually use the remote name asked from the user

Broken since introduction in cad37e19 ("dim: auto-add remotes"), the
remote asked from the user gets ignored. Get the remote name to the
remote variable. Also bail out on non-zero returns from read.

Cc: Daniel Vetter <daniel@ffwll.ch>
Acked-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>