mm: hwpoison: Use compound_head() flags for huge pages

memory_failure() chooses a recovery action function based on the page flags.
For huge pages it uses the tail page flags which don't have anything
interesting set, resulting in:
> Memory failure: 0x9be3b4: Unknown page state
> Memory failure: 0x9be3b4: recovery action for unknown page: Failed

Instead, save a copy of the head page's flags if this is a huge page,
this means if there are no relevant flags for this tail page, we use
the head pages flags instead. This results in the me_huge_page()
recovery action being called:
> Memory failure: 0x9b7969: recovery action for huge page: Delayed

Signed-off-by: James Morse <james.morse@arm.com>