Documentation: leds: Remove .rst extension for leds-st1202 on index

No other LED driver is listed on index.rst with the extension .rst.
Remove it.

Fixes: b1816b22 ("Documentation:leds: Add leds-st1202.rst")
Signed-off-by: Manuel Fombuena <fombuena@outlook.com>
Link: https://lore.kernel.org/r/CWLP123MB5473137572529F99746F4AC4C5C32@CWLP123MB5473.GBRP123.PROD.OUTLOOK.COM


Signed-off-by: Lee Jones <lee@kernel.org>