isdn/gigaset: clarify gigaset_modem_fill control structure

Replace the flag-controlled retry loop by explicit goto statements
in the error branches to make the control structure easier to
understand.

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

diff --cc drivers/isdn/gigaset/usb-gigaset.c
Simple merge