ftrace: Check if pages were allocated before calling free_pages()

ftrace: Check if pages were allocated before calling free_pages()

It is possible that on error pg->size can be zero when getting its order,
which would return a -1 value. It is dangerous to pass in an order of -1
to free_pages(). Check if order is greater than or equal to zero before
calling free_pages().

Link: https://lore.kernel.org/lkml/[email protected]/
Reported-by: Abaci Robot <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>