powercap: fix sscanf() error return value handling

Fix inconsistent error handling for sscanf() return value check.

Implicit boolean conversion is used instead of explicit return
value checks. The code checks if (!sscanf(...)) which is incorrect
because:
1. sscanf returns the number of successfully parsed items
2. On success, it returns 1 (one item passed)
3. On failure, it returns 0 or EOF
4. The check 'if (!sscanf(...))' is wrong because it treats
success (1) as failure

All occurrences of sscanf() now uses explicit return value check.
With this behavior it returns '-EINVAL' when parsing fails (returns
0 or EOF), and continues when parsing succeeds (returns 1).

Signed-off-by: Sumeet Pawnikar <[e-mail]>
[ rjw: Subject and changelog edits ]
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/powercap/powercap_sys.c

···
 	int id; \
 	struct powercap_zone_constraint *pconst;\
 	\
-	if (!sscanf(dev_attr->attr.name, "constraint_%d_", &id)) \
+	if (sscanf(dev_attr->attr.name, "constraint_%d_", &id) != 1) \
 		return -EINVAL; \
 	if (id >= power_zone->const_id_cnt)	\
 		return -EINVAL; \
···
 	int id; \
 	struct powercap_zone_constraint *pconst;\
 	\
-	if (!sscanf(dev_attr->attr.name, "constraint_%d_", &id)) \
+	if (sscanf(dev_attr->attr.name, "constraint_%d_", &id) != 1) \
 		return -EINVAL; \
 	if (id >= power_zone->const_id_cnt)	\
 		return -EINVAL; \
···
 	ssize_t len = -ENODATA;
 	struct powercap_zone_constraint *pconst;
 
-	if (!sscanf(dev_attr->attr.name, "constraint_%d_", &id))
+	if (sscanf(dev_attr->attr.name, "constraint_%d_", &id) != 1)
 		return -EINVAL;
 	if (id >= power_zone->const_id_cnt)
 		return -EINVAL;