osxvideo: fix avfoundation device name

Fixes a bug introduced in "osxvideo: use avfoundation indev" where the
video device didn't have the right name.

Change-Id: Ib2b31191925e89b6478a61812667ed5f86acc5d2
Reviewed-by: Kateryna Kostiuk <kateryna.kostiuk@savoirfairelinux.com>