w1: Misuse of get_user()/put_user() reported by sparse

sparse warnings: (new ones prefixed by >>)
>> drivers/w1/slaves/w1_ds28e04.c:342:13: sparse: sparse: incorrect type in initializer (different address spaces) @@ expected char [noderef] __user *_pu_addr @@ got char *buf @@
drivers/w1/slaves/w1_ds28e04.c:342:13: sparse: expected char [noderef] __user *_pu_addr
drivers/w1/slaves/w1_ds28e04.c:342:13: sparse: got char *buf
>> drivers/w1/slaves/w1_ds28e04.c:356:13: sparse: sparse: incorrect type in initializer (different address spaces) @@ expected char const [noderef] __user *_gu_addr @@ got char const *buf @@
drivers/w1/slaves/w1_ds28e04.c:356:13: sparse: expected char const [noderef] __user *_gu_addr
drivers/w1/slaves/w1_ds28e04.c:356:13: sparse: got char const *buf

The buffer buf is a failsafe buffer in kernel space, it's not user
memory hence doesn't deserve the use of get_user() or put_user().

Access 'buf' content directly.

Link: https://lore.kernel.org/lkml/[e-mail]/T/
Reported-by: kernel test robot <[e-mail]>
Signed-off-by: Christophe Leroy <[e-mail]>
Link: https://lore.kernel.org/r/d14ed8d7[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/w1/slaves/w1_ds28e04.c

···
 module_param_named(strong_pullup, w1_strong_pullup, int, 0);
 
 /* enable/disable CRC checking on DS28E04-100 memory accesses */
-static char w1_enable_crccheck = 1;
+static bool w1_enable_crccheck = true;
 
 #define W1_EEPROM_SIZE		512
 #define W1_PAGE_COUNT		16
···
 static ssize_t crccheck_show(struct device *dev, struct device_attribute *attr,
 			     char *buf)
 {
-	if (put_user(w1_enable_crccheck + 0x30, buf))
-		return -EFAULT;
-
-	return sizeof(w1_enable_crccheck);
+	return sysfs_emit(buf, "%d\n", w1_enable_crccheck);
 }
 
 static ssize_t crccheck_store(struct device *dev, struct device_attribute *attr,
 			      const char *buf, size_t count)
 {
-	char val;
+	int err = kstrtobool(buf, &w1_enable_crccheck);
 
-	if (count != 1 || !buf)
-		return -EINVAL;
+	if (err)
+		return err;
 
-	if (get_user(val, buf))
-		return -EFAULT;
-
-	/* convert to decimal */
-	val = val - 0x30;
-	if (val != 0 && val != 1)
-		return -EINVAL;
-
-	/* set the new value */
-	w1_enable_crccheck = val;
-
-	return sizeof(w1_enable_crccheck);
+	return count;
 }
 
 static DEVICE_ATTR_RW(crccheck);