parisc: Fix fall-through warnings in fpudispatch.c

In fpudispatch.c we see a lot of fall-through warnings, but for this file we
prefer to not mark the switches and instead keep it in it's original state as
it's copied from HP-UX.

Fixes: a035d552 ("Makefile: Globally enable fall-through warning")
Signed-off-by: Helge Deller <deller@gmx.de>