media: soc_camera: fix compiler warning

In function 'strncpy',
    inlined from 'soc_camera_platform_probe' at drivers/media/platform/soc_camera/soc_camera_platform.c:162:2:
include/linux/string.h:246:9: warning: '__builtin_strncpy' specified bound 32 equals destination size [-Wstringop-truncation]
  return __builtin_strncpy(p, q, size);
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>