selftests: efivarfs: remove the test_create_read file if it was exist

After the first run, the test case 'test_create_read' will always
fail because the file is exist and file's attr is 'S_IMMUTABLE',
open with 'O_RDWR' will always return -EPERM.

Signed-off-by: ZhangXiaoxu <zhangxiaoxu5@huawei.com>
Signed-off-by: Shuah Khan <shuah@kernel.org>

tools/testing/selftests/efivarfs/efivarfs.sh

@@ -77,6 +77,10 @@ test_create_empty()
 test_create_read()
 {
 	local file=$efivarfs_mount/$FUNCNAME-$test_guid
+	if [ -f $file]; then
+		chattr -i $file
+		rm -rf $file
+	fi
 	./create-read $file
 }