Update the error condition to reflect actual usecase -
an unsized array is declared in a shader other than tessellation shader.

Bug: angleproject:5557
Test: KHR-GLES32.core.texture_cube_map_array.texture_size_tesselation_con_sh
Change-Id: I3547f52a26a5c450ac7b6df65d026c3c38f7c71d
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2823576
Commit-Queue: Mohan Maiya <m.maiya@samsung.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>