backlight: led_bl: Hold led_access lock when calling led_sysfs_disable()

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

backlight: led_bl: Hold led_access lock when calling led_sysfs_disable()

Lockdep detects the following issue on led-backlight removal:

[ 142.315935] ------------[ cut here ]------------

[ 142.315954] WARNING: CPU: 2 PID: 292 at drivers/leds/led-core.c:455 led_sysfs_enable+0x54/0x80

...

[ 142.500725] Call trace:

[ 142.503176] led_sysfs_enable+0x54/0x80 (P)

[ 142.507370] led_bl_remove+0x80/0xa8 [led_bl]

[ 142.511742] platform_remove+0x30/0x58

[ 142.515501] device_remove+0x54/0x90

...

Indeed, led_sysfs_enable() has to be called with the led_access

lock held.

Hold the lock when calling led_sysfs_disable().