firmware: use let-else clause to improve code readability on `merge_sections` function

Signed-off-by: Zhouqi Jiang <luojia@hust.edu.cn>

src/firmware.rs

@@ -41,7 +41,9 @@ pub enum Firmware {
 impl Firmware {
     /// Merge sections, and fill gap with 0xff
     pub fn merge_sections(self) -> Result<Self> {
-        if let Firmware::Sections(mut sections) = self {
+        let Firmware::Sections(mut sections) = self else {
+            return Ok(self);
+        };
         sections.sort_by_key(|s| s.address);
         let mut merged = vec![];
 
@@ -67,9 +69,6 @@ impl Firmware {
         }
         merged.push(last);
         Ok(Firmware::Sections(merged))
-        } else {
-            Ok(self)
-        }
     }
 }