nvmecontrol: fix wrong temperature unit for INTEL SSDs.

Although intel's specification did not tell which unit for Temperature
Statistics (Log Identifier C5h), I believe it is based on Celsius
instead of Kelvin.

here is my P3700 SSDs result(before):

Intel Temperature Log

Current: 30 K, -243.15 C, -405.67 F
Overtemp Last Flags 0
Overtemp Lifetime Flags 0
Max Temperature 53 K, -220.15 C, -364.27 F
Min Temperature 17 K, -256.15 C, -429.07 F
Max Operating Temperature 63 K, -210.15 C, -346.27 F
Min Operating Temperature 0 K, -273.15 C, -459.67 F
Estimated Temperature Offset: 0 C/K
after apply the patch, result is

Intel Temperature Log

Current: 303.15 K, 30 C, 86.00 F
Overtemp Last Flags 0
Overtemp Lifetime Flags 0
Max Temperature 326.15 K, 53 C, 127.40 F
Min Temperature 290.15 K, 17 C, 62.60 F
Max Operating Temperature 336.15 K, 63 C, 145.40 F
Min Operating Temperature 273.15 K, 0 C, 32.00 F
Estimated Temperature Offset: 0 C/K
I also compare to smartctl's report. it match very well.

also tested on Intel P3600, it fixed the problem.

Signed-off-by: Wanpeng Qian <wanpengqian@gmail.com>
Reviewed by: imp (added tweak to samsung.c so it still compiles)
Differential Revision: https://reviews.freebsd.org/D32845