thermal: Fix NULL pointer dereferences in of_thermal_ functions

In the Linux kernel, the following vulnerability has been resolved:

thermal: Fix NULL pointer dereferences in of_thermal_ functions

of_parse_thermal_zones() parses the thermal-zones node and registers a

thermal_zone device for each subnode. However, if a thermal zone is

consuming a thermal sensor and that thermal sensor device hasn't probed

yet, an attempt to set trip_point_*_temp for that thermal zone device

can cause a NULL pointer dereference. Fix it.

console:/sys/class/thermal/thermal_zone87 # echo 120000 > trip_point_0_temp

...

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000020

...

Call trace:

of_thermal_set_trip_temp+0x40/0xc4

trip_point_temp_store+0xc0/0x1dc

dev_attr_store+0x38/0x88

sysfs_kf_write+0x64/0xc0

kernfs_fop_write_iter+0x108/0x1d0

vfs_write+0x2f4/0x368

ksys_write+0x7c/0xec

__arm64_sys_write+0x20/0x30

el0_svc_common.llvm.7279915941325364641+0xbc/0x1bc

do_el0_svc+0x28/0xa0

el0_svc+0x14/0x24

el0_sync_handler+0x88/0xec

el0_sync+0x1c0/0x200

While at it, fix the possible NULL pointer dereference in other

functions as well: of_thermal_get_temp(), of_thermal_set_emul_temp(),

of_thermal_get_trend().