svga: change PIPE_CAPF_MAX_TEXTURE_LOD_BIAS from 16.0 to 15.0

The legal range for the device is apparently [-16.0, +15.0].
Limiting the range to [-15, +15] fixes piglit's lodbias test.

NOTE: This is a candidate for the 8.0 branch.

Reviewed-by: José Fonseca <jfonseca@vmware.com>

src/gallium/drivers/svga/svga_screen.c

@@ -120,7 +120,7 @@ svga_get_paramf(struct pipe_screen *screen, enum pipe_capf param)
       return result.u;
 
    case PIPE_CAPF_MAX_TEXTURE_LOD_BIAS:
-      return 16.0;
+      return 15.0;
 
    default:
       return 0;