nir: Update the comment about nir_lower_uniforms_to_ubo()'s multiplier.

I remembered doing this analysis and was arguing in another MR that this
pass didn't have any driver dependency, but it actually does based on
PIPE_CAP_PACKED_UNIFORMS.

Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Reviewed-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6359>

src/compiler/nir/nir_lower_uniforms_to_ubo.c

@@ -26,13 +26,16 @@
  * Simultaneously, remap existing UBO accesses by increasing their binding
  * point by 1.
  *
- * Both the base and the offset are interpreted as 16-byte units.
+ * Note that nir_intrinsic_load_uniform base/ranges can be set in different
+ * units, and the multiplier argument caters to supporting these different
+ * units.
  *
- * Note that locations can be set in different units, and the multiplier
- * argument caters to supporting these different units.
  * For example:
- * - st_glsl_to_nir uses dwords (4 bytes) so the multiplier should be 4
- * - tgsi_to_nir uses bytes, so the multiplier should be 16
+ * - st_glsl_to_nir for PIPE_CAP_PACKED_UNIFORMS uses dwords (4 bytes) so the
+ *   multiplier should be 4
+ * - st_glsl_to_nir for !PIPE_CAP_PACKED_UNIFORMS uses vec4s so the
+ *   multiplier should be 16
+ * - tgsi_to_nir uses vec4s, so the multiplier should be 16
  */
 
 #include "nir.h"