[AArch64] Require aarch64_sve256_hw for a 256-bit SVE test

One of the SVE run tests was specific to 256-bit SVE but tried to
run for all SVE lengths.

2020-01-10  Richard Sandiford  <richard.sandiford@arm.com>

gcc/testsuite/
	* gcc.target/aarch64/sve/index_1_run.c: Require aarch64_sve256_hw
	rather than aarch64_sve_hw.

From-SVN: r280104

gcc/testsuite/ChangeLog

+2020-01-10  Richard Sandiford  <richard.sandiford@arm.com>
+
+	* gcc.target/aarch64/sve/index_1_run.c: Require aarch64_sve256_hw
+	rather than aarch64_sve_hw.
+
 2020-01-10  Richard Biener  <rguenther@suse.de>
 
 	PR testsuite/93216

gcc/testsuite/gcc.target/aarch64/sve/index_1_run.c

-/* { dg-do run { target aarch64_sve_hw } } */
+/* { dg-do run { target aarch64_sve256_hw } } */
 /* { dg-options "-O2 -ftree-vectorize -msve-vector-bits=256" } */
 
 #include "index_1.c"