target-tricore: properly fix dvinit_b/h_13

The TriCore documentation was wrong on how to calculate ovf bits for those two
instructions, which I confirmed with real hardware (TC1796 chip). An ovf
actually happens, if the result (without remainder) does not fit into 8/16 bits.

Signed-off-by: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>