Suppress implicit-fallthrough warnings.

Add FALLTHROUGH_INTENDED for clang compiler.

Bug: 112564944
Test: build with global -Wimplicit-fallthrough.
Change-Id: Iedf7e46445101a5e3358473e1200212d67cf58d1
diff --git a/stack/gatt/gatt_sr.cc b/stack/gatt/gatt_sr.cc
index 67c5db9..4ca516d 100644
--- a/stack/gatt/gatt_sr.cc
+++ b/stack/gatt/gatt_sr.cc
@@ -884,13 +884,13 @@
       sr_data.write_req.is_prep = true;
       STREAM_TO_UINT16(sr_data.write_req.offset, p);
       len -= 2;
-    /* fall through */
+      FALLTHROUGH_INTENDED; /* FALLTHROUGH */
     case GATT_SIGN_CMD_WRITE:
       if (op_code == GATT_SIGN_CMD_WRITE) {
         VLOG(1) << "Write CMD with data sigining";
         len -= GATT_AUTH_SIGN_LEN;
       }
-    /* fall through */
+      FALLTHROUGH_INTENDED; /* FALLTHROUGH */
     case GATT_CMD_WRITE:
     case GATT_REQ_WRITE:
       if (op_code == GATT_REQ_WRITE || op_code == GATT_REQ_PREPARE_WRITE)