NFC: st21nfca: Fix fall-through warnings

NFC: st21nfca: Fix fall-through warnings

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

This patch fixes the following warnings by adding a missing break
and a fall-through annotation:

drivers/nfc/st21nfca/dep.c: In function ‘st21nfca_tm_event_send_data’:
drivers/nfc/st21nfca/dep.c:391:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
   switch (cmd1) {
   ^~~~~~
drivers/nfc/st21nfca/dep.c:404:2: note: here
  default:
  ^~~~~~~
In file included from ./include/linux/kernel.h:15,
                 from ./include/linux/skbuff.h:17,
                 from ./include/net/nfc/hci.h:21,
                 from drivers/nfc/st21nfca/dep.c:17:
drivers/nfc/st21nfca/dep.c: In function ‘st21nfca_im_recv_dep_res_cb’:
./include/linux/printk.h:303:2: warning: this statement may fall through [-Wimplicit-fallthrough=]
  printk(KERN_ERR pr_fmt(fmt), ##__VA_ARGS__)
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/nfc/st21nfca/dep.c:622:4: note: in expansion of macro ‘pr_err’
    pr_err("Received a ACK/NACK PDU\n");
    ^~~~~~
drivers/nfc/st21nfca/dep.c:623:3: note: here
   case ST21NFCA_NFC_DEP_PFB_I_PDU:
   ^~~~

Warning level 3 was used: -Wimplicit-fallthrough=3

This patch is part of the ongoing efforts to enable
-Wimplicit-fallthrough.

Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>