lavc/dxva2_internal: Cast the dxva2 and d3d11 decoders and cfgs to (void *).

Silences several warnings:
libavcodec/dxva2_internal.h:107:98: warning: pointer type mismatch in conditional expression
libavcodec/dxva2_internal.h:109:94: warning: pointer type mismatch in conditional expression

Reported-by: Reino Wijnsma

libavcodec/dxva2_internal.h

@@ -104,9 +104,9 @@ typedef struct FFDXVASharedContext {
 #if CONFIG_D3D11VA && CONFIG_DXVA2
 #define DXVA_CONTEXT_WORKAROUND(avctx, ctx)     (ff_dxva2_is_d3d11(avctx) ? ctx->d3d11va.workaround : ctx->dxva2.workaround)
 #define DXVA_CONTEXT_COUNT(avctx, ctx)          (ff_dxva2_is_d3d11(avctx) ? ctx->d3d11va.surface_count : ctx->dxva2.surface_count)
-#define DXVA_CONTEXT_DECODER(avctx, ctx)        (ff_dxva2_is_d3d11(avctx) ? ctx->d3d11va.decoder : ctx->dxva2.decoder)
+#define DXVA_CONTEXT_DECODER(avctx, ctx)        (ff_dxva2_is_d3d11(avctx) ? (void *)ctx->d3d11va.decoder : (void *)ctx->dxva2.decoder)
 #define DXVA_CONTEXT_REPORT_ID(avctx, ctx)      (*(ff_dxva2_is_d3d11(avctx) ? &ctx->d3d11va.report_id : &ctx->dxva2.report_id))
-#define DXVA_CONTEXT_CFG(avctx, ctx)            (ff_dxva2_is_d3d11(avctx) ? ctx->d3d11va.cfg : ctx->dxva2.cfg)
+#define DXVA_CONTEXT_CFG(avctx, ctx)            (ff_dxva2_is_d3d11(avctx) ? (void *)ctx->d3d11va.cfg : (void *)ctx->dxva2.cfg)
 #define DXVA_CONTEXT_CFG_BITSTREAM(avctx, ctx)  (ff_dxva2_is_d3d11(avctx) ? ctx->d3d11va.cfg->ConfigBitstreamRaw : ctx->dxva2.cfg->ConfigBitstreamRaw)
 #define DXVA_CONTEXT_CFG_INTRARESID(avctx, ctx) (ff_dxva2_is_d3d11(avctx) ? ctx->d3d11va.cfg->ConfigIntraResidUnsigned : ctx->dxva2.cfg->ConfigIntraResidUnsigned)
 #define DXVA_CONTEXT_CFG_RESIDACCEL(avctx, ctx) (ff_dxva2_is_d3d11(avctx) ? ctx->d3d11va.cfg->ConfigResidDiffAccelerator : ctx->dxva2.cfg->ConfigResidDiffAccelerator)