USB: Kconfig: fix typos in USB_FUNCTIONFS* description

It's spelled "Function Filesystem" / "FunctionFS". This patch
fixes some typos (FunctioFS->FunctionFS, Funcion->Function,
funcion->function, redundant "as") in the Kconfig description of
USB_FUNCTIONFS*.

Signed-off-by: Michael Prokop <mika@grml.org>
Acked-by: Michal Nazarewicz <m.nazarewicz@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>