Don't leak lock from os_kmem_alloc().

[jhb]

Summary

The current port patches for os_kmem_alloc() add VM object locking.
However, the lock is not unlocked in the success case because the
unlock code is inside of an if body instead of after the if statement.

Test Plan

• jpaetzel@ confirmed this fixed a panic he was seeing on head. The panic was a WITNESS warning about the lock still being held when an ithread suspended.

[jpaetzel]

The path for the file to be patched is wrong, the original is correct in this case. The code change does fix the kernel panic when the module is loaded.

[jhb]

• Fix file path.

[jpaetzel]

LGTM

[swills]

Approved, thanks!