[PATCH] ARC: kgdb: add 'fallthrough' to prevent a warning

[Randy Dunlap]

Use the 'fallthrough' macro to document that this switch case
does indeed fall through to the next case.

../arch/arc/kernel/kgdb.c: In function 'kgdb_arch_handle_exception':
../arch/arc/kernel/kgdb.c:141:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
  141 |   if (kgdb_hex2long(&ptr, &addr))
      |      ^
../arch/arc/kernel/kgdb.c:144:2: note: here
  144 |  case 'D':
      |  ^~~~

Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: Vineet Gupta <vgupta@xxxxxxxxxxxx>
Cc: linux-snps-arc@xxxxxxxxxxxxxxxxxxx
---
 arch/arc/kernel/kgdb.c |    1 +
 1 file changed, 1 insertion(+)

--- linux-next-20210420.orig/arch/arc/kernel/kgdb.c
+++ linux-next-20210420/arch/arc/kernel/kgdb.c
@@ -140,6 +140,7 @@ int kgdb_arch_handle_exception(int e_vec
 		ptr = &remcomInBuffer[1];
 		if (kgdb_hex2long(&ptr, &addr))
 			regs->ret = addr;
+		fallthrough;
 
 	case 'D':
 	case 'k':