hwmon: (ibmpowernv) Silence strncpy() warning

hwmon: (ibmpowernv) Silence strncpy() warning

Fixes the following W=1 kernel build warning(s):

 from drivers/hwmon/ibmpowernv.c:11:
 In function ‘strncpy’,
 inlined from ‘get_sensor_index_attr’ at drivers/hwmon/ibmpowernv.c:243:2,
 inlined from ‘create_device_attrs’ at drivers/hwmon/ibmpowernv.c:280:8:
 include/linux/string.h:297:30: warning: ‘__builtin_strncpy’ specified bound 32 equals destination size [-Wstringop-truncation]
 297 | #define __underlying_strncpy __builtin_strncpy
 | ^
 include/linux/string.h:307:9: note: in expansion of macro ‘__underlying_strncpy’
 307 | return __underlying_strncpy(p, q, size);
 | ^~~~~~~~~~~~~~~~~~~~

Cc: Jean Delvare <jdelvare@suse.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Neelesh Gupta <neelegup@linux.vnet.ibm.com>
Cc: linux-hwmon@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20201112095715.1993117-4-lee.jones@linaro.org
Signed-off-by: Guenter Roeck <linux@roeck-us.net>