winsys/svga: Fix incorrect type usage in IOCTL v2

winsys/svga: Fix incorrect type usage in IOCTL v2

While similar in layout, the size of the SVGA3dSize type may be smaller than
the struct drm_vmw_size type that is part of the ioctl interface. The kernel
driver could accordingly overwrite a memory area following the size variable
on the stack. Typically that would be another local variable, causing
breakage in, for example, ubuntu 12.04.5 where the handle local variable
becomes overwritten.

v2: Fix whitespace errors

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jakob Bornecrantz <jakob@vmware.com>
Cc: "10.1 10.2 10.3" <mesa-stable@lists.freedesktop.org>