While enabling best practices layer the struct that
gets added to the pNext chain is a stack variable and
goes out of scope beyond the if-check. Move the
struct variables out of local scope to prevent access
violation errors during vkCreateInstance.

Bug: b/156661359
Change-Id: Ifa470ff1e51d454782695adcf40b4db2aa1608a0
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2335747Reviewed-by: Cody Northrop <cnorthrop@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Mohan Maiya <m.maiya@samsung.com>