mesa: fix duplicate initializer
What does this MR do and why?
mesa: fix duplicate initializer
fixes warning with clang:
../src/mesa/main/spirv_capabilities.c:98:45: warning: initializer overrides prior initialization of this subobject [-Winitializer-overrides]
98 | .TransformFeedback = gl_exts->ARB_transform_feedback3,
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../src/mesa/main/spirv_capabilities.c:72:45: note: previous initialization is here
72 | .TransformFeedback = true,
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>