kbuild: fix call to adjust_autoksyms.sh when output directory specified

When a different output directory is specified during the build process (with
O= or KBUILD_OUTPUT), the call to adjust_autoksyms.sh script fails with the
following error:
/bin/sh scripts/adjust_autoksyms.sh \
	  "make KBUILD_MODULES=1 -f ../Makefile autoksyms_recursive"
	  /bin/sh: scripts/adjust_autoksyms.sh: No such file or directory
	  make[2]: *** [vmlinux] Error 127
	  make[1]: *** [sub-make] Error 2
	  make: *** [__sub-make] Error 2

Using the absolute path with $(srctree) variable solves the problem.

This is in case the CONFIG_TRIM_UNUSED_KSYMS option is specified.
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Fixes: 23121ca2 ("kbuild: create/adjust generated/autoksyms.h")
Cc: Nicolas Pitre <nico@linaro.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Michal Marek <mmarek@suse.com>

Makefile

@@ -934,7 +934,7 @@ quiet_cmd_link-vmlinux = LINK    $@
 # execute if the rest of the kernel build went well.
 vmlinux: scripts/link-vmlinux.sh $(vmlinux-deps) FORCE
 ifdef CONFIG_TRIM_UNUSED_KSYMS
-	$(Q)$(CONFIG_SHELL) scripts/adjust_autoksyms.sh \
+	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/adjust_autoksyms.sh \
 	  "$(MAKE) KBUILD_MODULES=1 -f $(srctree)/Makefile autoksyms_recursive"
 endif
 ifdef CONFIG_HEADERS_CHECK
@@ -949,13 +949,13 @@ endif
 	+$(call if_changed,link-vmlinux)
 
 autoksyms_recursive: $(vmlinux-deps)
-	$(Q)$(CONFIG_SHELL) scripts/adjust_autoksyms.sh \
+	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/adjust_autoksyms.sh \
 	  "$(MAKE) KBUILD_MODULES=1 -f $(srctree)/Makefile autoksyms_recursive"
 PHONY += autoksyms_recursive
 
 # standalone target for easier testing
 include/generated/autoksyms.h: FORCE
-	$(Q)$(CONFIG_SHELL) scripts/adjust_autoksyms.sh true
+	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/adjust_autoksyms.sh true
 
 # Build samples along the rest of the kernel
 ifdef CONFIG_SAMPLES