mfd: omap-usb-host: Remove invalid use of kerneldoc syntax

Kerneldoc is for documenting function arguments and return values.

Prevents warnings like:

 drivers/mfd/omap-usb-host.c:128: warning: cannot understand function prototype: 'const char * const port_modes[] = '

Cc: Tony Lindgren <tony@atomide.com>
Cc: Keshava Munegowda <keshava_mgowda@ti.com>
Cc: Roger Quadros <rogerq@ti.com>
Cc: linux-omap@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>