drivers/isdn/hardware/eicon/debug.c: fix uninitialized var warning

drivers/isdn/hardware/eicon/debug.c: In function 'SuperTraceASSIGN':
drivers/isdn/hardware/eicon/debug.c:1191: warning: 'rx_dma_magic' may be used uninitialized in this function

Cc: Karsten Keil <kkeil@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>