hwmon: (w83627ehf) Fix crash seen with W83627DHG-P

Loading the driver on a system with W83627DHG-P crashes as follows.

w83627ehf: Found W83627DHG-P chip at 0x290
BUG: kernel NULL pointer dereference, address: 0000000000000000
PGD 0 P4D 0
Oops: 0000 [#1] SMP NOPTI
CPU: 0 PID: 604 Comm: sensors Not tainted 5.6.0-rc2-00055-gca7e1fd1026c #29
Hardware name:  /D425KT, BIOS MWPNT10N.86A.0132.2013.0726.1534 07/26/2013
RIP: 0010:w83627ehf_read_string+0x27/0x70 [w83627ehf]
Code: [... ]
RSP: 0018:ffffb95980657df8 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff96caaa7f5218 RCX: 0000000000000000
RDX: 0000000000000015 RSI: 0000000000000001 RDI: ffff96caa736ec08
RBP: 0000000000000000 R08: ffffb95980657e20 R09: 0000000000000001
R10: ffff96caaa635cc0 R11: 0000000000000000 R12: ffff96caa9f7cf00
R13: ffff96caa9ec3d00 R14: ffff96caa9ec3d28 R15: ffff96caa9ec3d40
FS:  00007fbc7c4e2740(0000) GS:ffff96caabc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000129d58000 CR4: 00000000000006f0
Call Trace:
 ? cp_new_stat+0x12d/0x160
 hwmon_attr_show_string+0x37/0x70 [hwmon]
 dev_attr_show+0x14/0x50
 sysfs_kf_seq_show+0xb5/0x1b0
 seq_read+0xcf/0x460
 vfs_read+0x9b/0x150
 ksys_read+0x5f/0xe0
 do_syscall_64+0x48/0x190
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
...

Temperature labels are not always present. Adjust sysfs attribute
visibility accordingly.

Reported-by: Meelis Roos <mroos@linux.ee>
Suggested-by: Dr. David Alan Gilbert <linux@treblig.org>
Reviewed-by: Dr. David Alan Gilbert <linux@treblig.org>
Cc: Meelis Roos <mroos@linux.ee>
Cc: Dr. David Alan Gilbert <linux@treblig.org>
Fixes: 266cd58 ("hwmon: (w83627ehf) convert to with_info interface")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/w83627ehf.c

@@ -1346,8 +1346,13 @@ w83627ehf_is_visible(const void *drvdata, enum hwmon_sensor_types type,
 		/* channel 0.., name 1.. */
 		if (!(data->have_temp & (1 << channel)))
 			return 0;
-		if (attr == hwmon_temp_input || attr == hwmon_temp_label)
+		if (attr == hwmon_temp_input)
 			return 0444;
+		if (attr == hwmon_temp_label) {
+			if (data->temp_label)
+				return 0444;
+			return 0;
+		}
 		if (channel == 2 && data->temp3_val_only)
 			return 0;
 		if (attr == hwmon_temp_max) {