backlight: sky81452: Fix sky81452_bl_platform_data kernel-doc

Correct the struct name and add a short struct description to fix the
kernel-doc notation.

Prevents this kernel-doc warning:
drivers/video/backlight/sky81452-backlight.c:64: warning: expecting prototype for struct sky81452_platform_data. Prototype was for struct sky81452_bl_platform_data instead

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230113064118.30169-1-rdunlap@infradead.org