libdrm: drmGetMinorNameFromFd: Fix FreeBSD variant

Fix the FreeBSD variant by getting the node type represented by fd to deduce
the target minor name.
We then return the full /dev/dri/<minorname><id> version.

Fix: #41
Fixes: 6818a50b
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Emmanuel Vadot <manu@FreeBSD.org>