target-tricore: Fix bugs found by coverity

This fixes one bug and one false positive found by coverity. The bug is,
that gen_mtcr was missing a mask to check the flag, which resulted in dead code.

The false positive is a intentional missing break for a jump and link address
insn followed by a jump and link insn. This adds a fall through comment to avoid
the false positive in the future.

Reported-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
