Fix issues found by static analysis

Fix issues found by static analysis

All of the issues that this patch fixes should not occur in practice,
but make the code a bit more robust. For example, this patch
default-initializes structures passed to Vulkan for initialization.
Normally, initialization should be done by the Vulkan entrypoint,
so it should be fine not initializing the structure as long as the
Vulkan API entrypoint exits with success status. It is still a good
idea to default-initialize anyway to make the behaviour deterministic
in cases where something is wrong in the system. All changes made
should have a negligible impact on performance for typical
applications.

Change-Id: Ia606ad2d3ea1627f9dfef0cadf93c7468ab568d8
Signed-off-by: Matteo Franchin <matteo.franchin@arm.com>