Fix the memory stomp running *core.internalformat.texture2d.depth_stencil*

Fix the memory stomp running *core.internalformat.texture2d.depth_stencil*

On QNX, we hit "Malloc Check Failed" and crash running CTS 3.2.5.0 with,
Test case 'KHR-GLES*.core.internalformat.texture2d.depth_stencil_unsigned_int_24_8_depth24_stencil8'..
Malloc Check Failed: :/builds/workspace/sdp700/build_aarch64/lib/c/alloc/dlist.c:1134

In InternalformatCaseBase::convertUInt_24_8(), two unsigned int data were modified
instead of one, which led to memory stomp and crash during the returning of function
InternalformatCaseBase::generateTextureData(). Rewrite function convertUInt_24_8()
to properly convert float color vec to unsigned_int_24_8_depth24_stencil8.

Affects:
KHR-GLES*.core.internalformat.texture2d.depth_stencil_unsigned_int_24_8_depth24_stencil8

Compoments: OpenGL

VK-GL-CTS issue: 1329

Change-Id: I95dfa2be272136e7ecf71b4ef49b43b90813f077