i965: Fix missing type in local variable declaration.

Trivial.  Fixes the following compiler warning (from GCC 5.1.0):

brw_context.c:629:10: warning: type defaults to ‘int’ in declaration
of ‘simd_size’ [-Wimplicit-int]

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/brw_context.c

@@ -626,7 +626,7 @@ brw_adjust_cs_context_constants(struct brw_context *brw)
     * is not always true. This allows us to run more test cases, and will be
     * required based on desktop GL compute shader requirements.
     */
-   const simd_size = ctx->API == API_OPENGL_CORE ? 16 : 8;
+   const int simd_size = ctx->API == API_OPENGL_CORE ? 16 : 8;
 
    const uint32_t max_invocations = simd_size * brw->max_cs_threads;
    ctx->Const.MaxComputeWorkGroupSize[0] = max_invocations;