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>

Author: javiercarrascocruz

drivers/mfd/omap-usb-tll.c

@@ -98,8 +98,8 @@
 
 struct usbtll_omap {
 	void __iomem	*base;
-	int		nch;		/* num. of channels */
-	struct clk	*ch_clk[];	/* must be the last member */
+	int		nch;
+	struct clk	*ch_clk[] __counted_by(nch);
 };
 
 /*-------------------------------------------------------------------------*/