pci: avoid compiler warning in quirks.c

Introduced by commit 5b889bf2

 ("PCI: Fix build if quirks are not
enabled"), which made the pci_dev_reset_methods[] array static and
'const', but didn't then change the code to match, and use a const
pointer when moving it to quirks.c.

Trivially fixed by just adding the required 'const' to the iterator
variable.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>