mfd: omap-usb-tll: Annotate struct usbtll_omap with __counted_by

mfd: omap-usb-tll: Annotate struct usbtll_omap with __counted_by

Use the __counted_by compiler attribute for the "struct clk *ch_clk[]"
flexible array member to improve the results of array bound sanitizers.

The comments for the variables are no longer needed as it is now clear
what is what.

Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Link: https://lore.kernel.org/r/20240620-omap-usb-tll-counted_by-v1-1-77797834bb9a@gmail.com
Signed-off-by: Lee Jones <lee@kernel.org>