sparc64: fix fall-through annotation

Replace "fallthru" with a proper "fall through" annotation.

This fix is part of the ongoing efforts to enabling
-Wimplicit-fallthrough
Signed-off-by: NGustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

arch/sparc/kernel/kgdb_64.c

@@ -148,7 +148,7 @@ int kgdb_arch_handle_exception(int e_vector, int signo, int err_code,
 			linux_regs->tpc = addr;
 			linux_regs->tnpc = addr + 4;
 		}
-		/* fallthru */
+		/* fall through */
 
 	case 'D':
 	case 'k':