gigaset: get rid of info() and warn() macros

Join the move away from the obsolete info() macro, opencoding the
remaining uses. While we're at it, also get rid of the warn() macro
by promoting the three remaining uses to err().

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