In gigaset_isdn_regdev, the name field may not have a null terminator
if the source string's length is equal to the buffer size.
Fix by zero filling the structure and excluding the last byte of the
name field from the copy.

Spotted with Coverity.
Signed-off-by: Tilman Schmidt <tilman@imap.cc>
Signed-off-by: David S. Miller <davem@davemloft.net>