PCI: Remove useless WARN_ON() from devres

PCI's devres implementation contains a WARN_ON() which served to inform
users relying on the legacy devres iomap table that this table does not
support multiple mappings per BAR.

The WARN_ON() can be regarded as useless by now, since mapping a BAR
multiple times is legal behavior and old users of pcim_iomap_table(), the
accessor function for that table, did not break in the past PCI devres
cleanup. New PCI users will hopefully notice that pcim_iomap_table() is
deprecated and are unlikely to use it for mapping the same BAR multiple
times.

Moreover, WARN_ON()s create noisy, difficult to read error messages which
can be more confusing than helpful, since they don't inform the user about
what precisely the problem is.

Remove the WARN_ON().

Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Philipp Stanner <phasta@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/20251218092819.149665-2-phasta@kernel.org