thermal: fix potential out-of-bounds memory access

temp_crit.name and temp_input.name have a length of 16 bytes.  Using
THERMAL_NAME_LENGTH (20) as length parameter for snprintf() may result in
out-of-bounds memory accesses.  Replace it with sizeof().

Addresses Coverity #115679

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Cc: Len Brown <lenb@kernel.org>
Cc: "Brown, Len" <len.brown@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>