libprefetch: fix regex to match 5.x/6.x ftrace event format

`mm_filemap_add_to_page_cache` event has a different formatting
depending on whether the version of kernel is 5.x or 6.x.

1. 5.x has a `page=` section after inode, while 6.x does not.
2. 6.x has a `order=` section at the end, while 5.x does not.

Current regex only matches to 6.x versions, which causes `cargo test`
to fail as the test uses 5.x format for testing.

Fix the regex to match on both existing 5.x test input, and newly
added 6.x test input.

Bug: 365889232
Test: `cargo test` passes with mixed 5.x and 6.x test input
Test: on emulator with 6.6 kernel, observe that pack file is
generated correctly.

Change-Id: I869b5570e4d1cb2c155eceb3fd00c177ed4676f6