[AArch64] Tweak sve/vcond_6.c test

[AArch64] Tweak sve/vcond_6.c test

sve/vcond_6.c was effectively testing a three-input logical operation,
since the result of BINOP needed to be ANDed with the loop predicate
before loading src[i].  This patch makes it really test a binary
operation instead.  A later patch will add (and optimise) the
three-operand case.

2018-05-08  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/testsuite/
	* gcc.target/aarch64/sve/vcond_6.c (LOOP): Unconditionally
	load from src[i].

From-SVN: r260028