check_aosp_license: Fix argument parser

Fixes the error:
```
[FAILED] aosp_license hook
    Traceback (most recent call last):
      File "/**/tools/repohooks/tools/check_aosp_license.py", line 108, in <module>
        sys.exit(main(sys.argv[1:]))
                 ^^^^^^^^^^^^^^^^^^
      File "/**/tools/repohooks/tools/check_aosp_license.py", line 93, in main
        file_paths = opts.file_paths
                     ^^^^^^^^^^^^^^^
    AttributeError: 'Namespace' object has no attribute 'file_paths'
```

Bug: 385205945
Test: repo upload -n with the aosp_license check on

Change-Id: I906d50f78cd7a87544ef3fc805a94eca286c177a
Reviewed-on: https://android-review.googlesource.com/c/platform/tools/repohooks/+/3427922
Lint: Lint 🤖 <ayeaye-gerrit@google.com>
Open-Source-Licensing: Lint 🤖 <ayeaye-gerrit@google.com>
Presubmit-Verified: Treehugger Robot <android-test-infra-workplan-finisher@system.gserviceaccount.com>
Reviewed-by: Mike Frysinger <vapier@google.com>
Reviewed-by: Jie Jiang <jiejiang@google.com>
Performance: CrystalBall Performance Presubmit <android-crystalball-presubmit-eng@google.com>

tools/check_aosp_license.py

diff --git a/tools/check_aosp_license.py b/tools/check_aosp_license.py
index 81fadb5..ffeed21 100755
--- a/tools/check_aosp_license.py
+++ b/tools/check_aosp_license.py
@@ -90,7 +90,7 @@
     parser = get_parser()
     opts = parser.parse_args(argv)
     commit_hash = opts.commit_hash
-    file_paths = opts.file_paths
+    file_paths = opts.files
 
     all_passed = True
     for file_path in file_paths: