In some error cases in hv_pci_probe(), allocated resources are not freed.

Fix this by adding a field to keep track of the high water mark for slots
that have resources allocated to them.  In case of an error, this high
water mark is used to know which slots have resources that must be released.
Since slots are numbered starting with zero, a value of -1 indicates no
slots have been allocated resources.  There may be unused slots in the range
between slot 0 and the high water mark slot, but these slots are already
ignored by the existing code in the allocate and release loops with the call
to get_pcichild_wslot().

Link: https://lore.kernel.org/r/20200507050211.10923-1-weh@microsoft.comSigned-off-by: Wei Hu <weh@microsoft.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>