staging: rts5208: remove unneeded header include path

A header include path without $(srctree)/ is suspicous because it does
not work with O= builds.

I can build drivers/staging/rts5208/ without this include path.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Link: https://lore.kernel.org/r/20200104163710.21582-1-masahiroy@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rts5208/Makefile

 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_RTS5208) := rts5208.o
 
-ccflags-y := -Idrivers/scsi
-
 rts5208-y := rtsx.o rtsx_chip.o rtsx_transport.o rtsx_scsi.o \
 	rtsx_card.o general.o sd.o xd.o ms.o spi.o