use asm::udf in panic-log

to match panic-probe behavior
UDF makes probe-run exit with a non-zero exit code

common/panic-log/src/lib.rs

@@ -8,7 +8,6 @@ use cortex_m::asm;
 fn panic(info: &PanicInfo) -> ! {
     log::error!("{}", info);
 
-    loop {
-        asm::bkpt()
-    }
+    // abort instruction: triggers a HardFault exception which causes probe-run to exit
+    asm::udf()
 }