riscv: avoid sending a SIGTRAP to a user thread trapped in WARN()

On RISC-V, when the kernel runs code on behalf of a user thread, and the
kernel executes a WARN() or WARN_ON(), the user thread will be sent
a bogus SIGTRAP.  Fix the RISC-V kernel code to not send a SIGTRAP when
a WARN()/WARN_ON() is executed.

Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
[paul.walmsley@sifive.com: fixed subject]
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>

arch/riscv/kernel/traps.c

@@ -134,7 +134,7 @@ asmlinkage void do_trap_break(struct pt_regs *regs)
 			break;
 		case BUG_TRAP_TYPE_WARN:
 			regs->sepc += get_break_insn_length(regs->sepc);
-			break;
+			return;
 		case BUG_TRAP_TYPE_BUG:
 #endif /* CONFIG_GENERIC_BUG */
 		default: