powerpc/fadump: Use swap() instead of open coding it

Clean the following coccicheck warning:

./arch/powerpc/kernel/fadump.c:1291:34-35: WARNING opportunity for
swap().
Reported-by: NAbaci Robot <abaci@linux.alibaba.com>
Signed-off-by: NJiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: NChristophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220129034847.76902-1-jiapeng.chong@linux.alibaba.com

arch/powerpc/kernel/fadump.c

@@ -1285,7 +1285,6 @@ static void fadump_release_reserved_area(u64 start, u64 end)
 static void sort_and_merge_mem_ranges(struct fadump_mrange_info *mrange_info)
 {
 	struct fadump_memory_range *mem_ranges;
-	struct fadump_memory_range tmp_range;
 	u64 base, size;
 	int i, j, idx;
 
@@ -1300,11 +1299,8 @@ static void sort_and_merge_mem_ranges(struct fadump_mrange_info *mrange_info)
 			if (mem_ranges[idx].base > mem_ranges[j].base)
 				idx = j;
 		}
-		if (idx != i) {
-			tmp_range = mem_ranges[idx];
-			mem_ranges[idx] = mem_ranges[i];
-			mem_ranges[i] = tmp_range;
-		}
+		if (idx != i)
+			swap(mem_ranges[idx], mem_ranges[i]);
 	}
 
 	/* Merge adjacent reserved ranges */