pvattest: Use map_or and map_or_else

Replace 'match .. { Some(v) => y, None/_ => x }' statements with
'Option::map_or_else' and 'Option::map_or'. See
https://rust-lang.github.io/rust-clippy/master/index.html#option_if_let_else.

Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

rust/pvattest/src/cmd/check/firmware.rs

@@ -56,10 +56,9 @@ impl Display for Response {
             if self.valid { "" } else { "not " }
         )?;
 
-        match &self.reason {
-            Some(r) => write!(f, "\n  Reason: {r}\n  ReferenceId: {}", self.reference_id),
-            None => Ok(()),
-        }
+        self.reason.as_ref().map_or(Ok(()), |r| {
+            write!(f, "\n  Reason: {r}\n  ReferenceId: {}", self.reference_id)
+        })
     }
 }