Fix flashing on HiFive1. (#649)

Broken by #645. It probably broke some other uses as well, but it was
reported (and easy to reproduce) as an issue with flashing.

Change-Id: Ic1b579c1361442479ced14156102ce68ab232396
Signed-off-by: Tim Newsome <tim@sifive.com>

src/target/riscv/riscv-011.c

@@ -1113,6 +1113,9 @@ static int execute_resume(struct target *target, bool step)
 
 	LOG_DEBUG("step=%d", step);
 
+	if (riscv_flush_registers(target) != ERROR_OK)
+		return ERROR_FAIL;
+
 	maybe_write_tselect(target);
 
 	/* TODO: check if dpc is dirty (which also is true if an exception was hit