selftests: drivers: Fix incorrect kernel headers search path

Use $(KHDR_INCLUDES) as lookup path for kernel headers. This prevents
building against kernel headers from the build environment in scenarios
where kernel headers are installed into a specific output directory
(O=...).
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: linux-kselftest@vger.kernel.org
Cc: Ingo Molnar <mingo@redhat.com>
Cc: <stable@vger.kernel.org>  # 5.18+
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/drivers/dma-buf/Makefile

 # SPDX-License-Identifier: GPL-2.0-only
-CFLAGS += -I../../../../../usr/include/
+CFLAGS += $(KHDR_INCLUDES)
 
 TEST_GEN_PROGS := udmabuf
 

tools/testing/selftests/drivers/s390x/uvdevice/Makefile

@@ -11,10 +11,9 @@ else
 TEST_GEN_PROGS := test_uvdevice
 
 top_srcdir ?= ../../../../../..
-khdr_dir = $(top_srcdir)/usr/include
 LINUX_TOOL_ARCH_INCLUDE = $(top_srcdir)/tools/arch/$(ARCH)/include
 
-CFLAGS += -Wall -Werror -static -I$(khdr_dir) -I$(LINUX_TOOL_ARCH_INCLUDE)
+CFLAGS += -Wall -Werror -static $(KHDR_INCLUDES) -I$(LINUX_TOOL_ARCH_INCLUDE)
 
 include ../../../lib.mk