[PATCH][binutils][AArch64] Fix diagnostic error message for structural load/store by element.

[Nick Clifton]

Hi Barnaby,

> 2019-06-26  Barnaby Wilks  <barnaby.wilks@arm.com>
> 
> 	* config/tc-aarch64.c (parse_operands): Add error check.
> 	* testsuite/gas/aarch64/diagnostic.l: New test.
> 	* testsuite/gas/aarch64/diagnostic.s: New test.
> 	* testsuite/gas/aarch64/illegal.l: New tests.
> 	* testsuite/gas/aarch64/illegal.s: New tests.

Approved and applied.

Cheers
  Nick