testsuite/110763: Ensure zero return from test

testsuite/110763: Ensure zero return from test

The test deliberately reads beyond bounds to exersize ubsan and the
return value may be anything, based on previous allocations.  The OFF
test caters for it by ANDing the return with 0, do the same for the DYN
test.

gcc/testsuite/ChangeLog:

	PR testsuite/110763
	* gcc.dg/ubsan/object-size-dyn.c (dyn): New parameter RET.
	(main): Use it.

Signed-off-by: Siddhesh Poyarekar <siddhesh@gotplt.org>