sbitmap: initialize weight to zero

Variable weight is not being initialized to zero before it is
used to compute the weight sum. Ensure it is initialized to zero.

Found with static analysis with cppcheck:
[lib/sbitmap.c:177]: (error) Uninitialized variable: weight
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

lib/sbitmap.c

@@ -169,7 +169,7 @@ EXPORT_SYMBOL_GPL(sbitmap_any_bit_clear);
 
 unsigned int sbitmap_weight(const struct sbitmap *sb)
 {
-	unsigned int i, weight;
+	unsigned int i, weight = 0;
 
 	for (i = 0; i < sb->map_nr; i++) {
 		const struct sbitmap_word *word = &sb->map[i];