ebreak should write mtval with 0, not pc

Resolves #426

The relevant passage in the spec does not mention software breakpoints
as one of the cases that cause mtval to be set to a nonzero value:

https://github.com/riscv/riscv-isa-manual/blob/274893e2f0365f904829bbb60fd05cc01d2bfb11/src/machine.tex#L2202

1 files changed, 1 insertions, 1 deletions

diff --git a/riscv/insns/ebreak.h b/riscv/insns/ebreak.h
index 736cebe..c22776c 100644
--- a/riscv/insns/ebreak.h
+++ b/riscv/insns/ebreak.h
@@ -1 +1 @@
-throw trap_breakpoint(pc);
+throw trap_breakpoint();