Documentation: leds: Update led-trigger-tty ABI description

Documentation: leds: Update led-trigger-tty ABI description

The 'led-trigger-tty' uses the same naming in the ABI documentation as
the 'led-trigger-netdev'. Which leads to the following warning when
building the documentation.

Warning: /sys/class/leds/<led>/rx is defined 2 times:
Documentation/ABI/testing/sysfs-class-led-trigger-tty:7
Documentation/ABI/testing/sysfs-class-led-trigger-netdev:49
Warning: /sys/class/leds/<led>/tx is defined 2 times:
Documentation/ABI/testing/sysfs-class-led-trigger-tty:15
Documentation/ABI/testing/sysfs-class-led-trigger-netdev:34

Renaming the 'What' path by prefixing it with 'tty_' solves this problem.

Fixes: 6dec659896b4 ("leds: ledtrig-tty: Add additional line state evaluation")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Florian Eckert <fe@dev.tdt.de>
Link: https://lore.kernel.org/r/20240110133410.81645-1-fe@dev.tdt.de
Signed-off-by: Lee Jones <lee@kernel.org>
(cherry picked from commit ea411a8422c1d7f8193d726fb76ba09534b6a5fe)
Signed-off-by: Lee Jones <lee@kernel.org>