m68k/amiserial: fix fallout of tty break handling rework

commit 9e98966c (tty: rework break handling)
forgot to update one exit point of rs_break() in the Amiga serial driver.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>