package/linux-tools/linux-tool-perf.mk.in: Fix disabling of documentation

We are trying to not build the perf documentation. However, the hook
being used to do so was named incorrectly. As a result, the build steps
to disable the documentation were never executed.

Rename the hook from
    LINUX_POST_PATCH_HOOKS
to
    LINUX_TOOLS_POST_PATCH_HOOKS
to fix the issue.

Fixes: 20b144666909 ("linux/tools: make it a real, separate package")
Signed-off-by: Markus Mayer <mmayer@broadcom.com>
Tested-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/linux-tools/linux-tool-perf.mk.in

@@ -126,7 +126,7 @@ define PERF_DISABLE_DOCUMENTATION
 		printf "%%:\n\t@:\n" >$(LINUX_DIR)/tools/perf/Documentation/GNUmakefile; \
 	fi
 endef
-LINUX_POST_PATCH_HOOKS += PERF_DISABLE_DOCUMENTATION
+LINUX_TOOLS_POST_PATCH_HOOKS += PERF_DISABLE_DOCUMENTATION
 
 # O must be redefined here to overwrite the one used by Buildroot for
 # out of tree build. We build perf in $(LINUX_DIR)/tools/perf/ and not just