mirage/mirage: PR #1585: add parens around the return value of register/register_arg

@1d07efa

Stages:

• ✔️ x86_64-debian-10-4.13 (7m25s)
• ✔️ arm64-debian-10-4.13 (6m41s)

History:

• 14/10/2024 12:36 ✔️ @1d07efa (7m25s)
• 14/10/2024 11:27 ✔️ @933bf8f (6m50s)
• 11/10/2024 15:46 ✔️ @ee2bf83 (1h56m)