ata: fixes kernel crash while tracing ata_eh_link_autopsy event
When tracing ata link error event, the kernel crashes when the disk is
removed due to NULL pointer access by trace_ata_eh_link_autopsy API.
This occurs as the dev is NULL when the disk disappeared. This patch
fixes this crash by calling trace_ata_eh_link_autopsy only if "dev"
is not NULL.
v2 changes:
Removed direct passing "link" pointer instead of "dev" in trace API.