drm/radeon/r300: Mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

Notice that in this particular case, I replaced "Pass through." with
"Fall through.", which is what GCC is expecting to find.

Addresses-Coverity-ID: 114734 ("Missing break in switch")
Addresses-Coverity-ID: 114735 ("Missing break in switch")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/r300.c

@@ -814,7 +814,7 @@ static int r300_packet0_check(struct radeon_cs_parser *p,
 					  ((idx_value >> 21) & 0xF));
 				return -EINVAL;
 			}
-			/* Pass through. */
+			/* Fall through. */
 		case 6:
 			track->cb[i].cpp = 4;
 			break;
@@ -965,7 +965,7 @@ static int r300_packet0_check(struct radeon_cs_parser *p,
 				return -EINVAL;
 			}
 			/* The same rules apply as for DXT3/5. */
-			/* Pass through. */
+			/* Fall through. */
 		case R300_TX_FORMAT_DXT3:
 		case R300_TX_FORMAT_DXT5:
 			track->textures[i].cpp = 1;