usb: gadget: Makefile: remove ccflags-y

No header file used from udc directory, so remove line below
ccflags-y += -I$(srctree)/drivers/usb/gadget/udc.

Signed-off-by: Linyu Yuan <quic_linyyuan@quicinc.com>
Link: https://lore.kernel.org/r/1647333751-32367-1-git-send-email-quic_linyyuan@quicinc.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>