usb: musb: update musb_platform_ops docs to match code

The "channel_program" member was renamed to "adjust_channel_params",
but the documentation wasn't updated.

Reported-by: Sergei Shtylyov <sshtylyov@mvista.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>