selftests/damon/_chk_dependency: get debugfs mount point from /proc/mounts

DAMON debugfs selftests dependency checker assumes debugfs would be
mounted at /sys/kernel/debug.  That would be ok for many cases, but some
systems might mounted the file system on some different places.  Parse the
real mount point using /proc/mounts file.

Link: https://lkml.kernel.org/r/20240207203134.69976-9-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/damon/_chk_dependency.sh

@@ -4,7 +4,14 @@
 # Kselftest framework requirement - SKIP code is 4.
 ksft_skip=4
 
-DBGFS=/sys/kernel/debug/damon
+DBGFS=$(grep debugfs /proc/mounts --max-count 1 | awk '{print $2}')
+if [ "$DBGFS" = "" ]
+then
+	echo "debugfs not mounted"
+	exit $ksft_skip
+fi
+
+DBGFS+="/damon"
 
 if [ $EUID -ne 0 ];
 then