Using EvqLast for the variable causes us to hit an assert in
sh::getQualifierString when we try to print a later error message.
Just use the appropriate qualifier regardless that it's not valid
for a compute shader, we've output the error.

Bug: angleproject:4187
Change-Id: If6fa5dea07d7b6e0d3307485f41d59c5ea7f1c4c
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1948525
Commit-Queue: Courtney Goeltzenleuchter <courtneygo@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>