Fix verifier upcasting type after instance_of.

The verifier automatically changed the type of a register to be
the checked type in an instance_of instruction, even if the
checked type was the register type's superclass. This would loosen
the type information of the register and cause problems later.

Bug: 10614872

Change-Id: I67aa2c66be754d946e928b8a64431f193539b842