Adjust expected output for bb-slp-21.c (PR 92527)

Adjust expected output for bb-slp-21.c (PR 92527)

After r278246, we can try building the out[] store value from scalars
if the target has no multiplication support.  That's not necessarily
a good thing, but like most of vect/, this test is run with the cost
model disabled.

2019-11-20  Richard Sandiford  <richard.sandiford@arm.com>

gcc/testsuite/
	PR testsuite/92527
	* gcc.dg/vect/bb-slp-21.c: Expect both SLP groups to be vectorized,
	regardless of whether the target supports multiplication.

From-SVN: r278531