[testsuite] fix array element count

[testsuite] fix array element count

This test is similar to pr103116-1.c, but instead of writing to
4*COUNT elements of x, it writes to 8*COUNT elements, but the
definition of x seems to have been adjusted along with the loop.  Fix
the array size so that it doesn't scribble over unrelated
statically-allocated objects.

for  gcc/testsuite/ChangeLog

	* gcc.dg/vect/pr103116-2.c (x): Fix array size.