selftests/x86/lam: Fix clean up fds in do_uring() and allocate_dsa_pasid()

selftests/x86/lam: Fix clean up fds in do_uring() and allocate_dsa_pasid()

Resolve minor fd leaks reported by cppcheck in lam.c.

Specifically, the 'file_fd' and 'fd' were not closed in do_uring()
and allocate_dsa_pasid() functions, respectively.

cppcheck output before this patch:

  tools/testing/selftests/x86/lam.c:685:3: error: Resource leak: file_fd [resourceLeak]
  tools/testing/selftests/x86/lam.c:693:3: error: Resource leak: file_fd [resourceLeak]
  tools/testing/selftests/x86/lam.c:1195:2: error: Resource leak: fd [resourceLeak]

cppcheck output after this patch:

  No resource leaks found

While this is a standalone test tool that doesn't really leak anything
in practice, as exit() cleans it up all, clean up resources nevertheless.

[ mingo: Updated the changelog. ]

Signed-off-by: Malaya Kumar Rout <malayarout91@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20250409135341.28987-1-malayarout91@gmail.com