i965: make brw_context::num_samples unsigned int

It is never a negative number. Variable is compared against unsigned
values and passed into functions that expect unsigned int.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

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

@@ -980,7 +980,7 @@ struct brw_context
     * Number of samples in ctx->DrawBuffer, updated by BRW_NEW_NUM_SAMPLES so
     * that we don't have to reemit that state every time we change FBOs.
     */
-   int num_samples;
+   unsigned int num_samples;
 
    /* BRW_NEW_URB_ALLOCATIONS:
     */