Fixes the following warning when loading the driver:
dahdi: Warning: Span DYN/eth/eth1/00:50:c2:97:92:1d/1 didn't specify a spantype. Please fix driver!
The spantype is intended to be used by the auto configuration tools
(dahdi_genconf, pinned spans, etc..) but dynamic spans, since they are created
directly by dahdi_cfg, never take part in the pre-registration auto
configuration, therefore the span type was never used.
Signed-off-by: Shaun Ruffell <sruffell@digium.com>