powerpc: fadump: use lock guard for mutex

use scoped_guard for scope based resource management of mutex.
This would make the code simpler and easier to maintain.

More details on lock guards can be found at
https://lore.kernel.org/all/20230612093537.614161713@infradead.org/T/#u

Reviewed-by: Srikar Dronamraju <srikar@linux.ibm.com>
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Reviewed-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250505075333.184463-4-sshegde@linux.ibm.com

Author: Shrikanth Hegde

arch/powerpc/kernel/fadump.c

@@ -1373,15 +1373,12 @@ static void fadump_free_elfcorehdr_buf(void)
 
 static void fadump_invalidate_release_mem(void)
 {
-	mutex_lock(&fadump_mutex);
-	if (!fw_dump.dump_active) {
-		mutex_unlock(&fadump_mutex);
-		return;
+	scoped_guard(mutex, &fadump_mutex) {
+		if (!fw_dump.dump_active)
+			return;
+		fadump_cleanup();
 	}
 
-	fadump_cleanup();
-	mutex_unlock(&fadump_mutex);
-
 	fadump_free_elfcorehdr_buf();
 	fadump_release_memory(fw_dump.boot_mem_top, memblock_end_of_DRAM());
 	fadump_free_cpu_notes_buf();