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 <sumeet4linux@gmail.com>
[ rjw: Subject and changelog edits ]
Link: https://patch.msgid.link/20251207151549.202452-1-sumeet4linux@gmail.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: sumeet4linux

drivers/powercap/powercap_sys.c

@@ -68,7 +68,7 @@ static ssize_t show_constraint_##_attr(struct device *dev, \
 	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; \
@@ -93,7 +93,7 @@ static ssize_t store_constraint_##_attr(struct device *dev,\
 	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; \
@@ -162,7 +162,7 @@ static ssize_t show_constraint_name(struct device *dev,
 	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;