PCI: Fix BUILD_BUG_ON usage for old gcc

As reported in the below link, it seems older versions of gcc cannot
determine that the howmany variable is known for all callers.  Include
a test so that newer compilers can enforce this sanity check and older
compilers can still work.  Add __always_inline attribute to give the
compiler an even better chance to know the inputs.

Link: https://lore.kernel.org/r/20250212185337.293023-1-alex.williamson@redhat.com
Fixes: 4453f36 ("PCI: Batch BAR sizing operations")
Reported-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/all/20250209154512.GA18688@redhat.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Oleg Nesterov <oleg@redhat.com>
Tested-by: Mitchell Augustin <mitchell.augustin@canonical.com>

Author: Alex Williamson

drivers/pci/probe.c

@@ -339,13 +339,14 @@ int __pci_read_base(struct pci_dev *dev, enum pci_bar_type type,
 	return (res->flags & IORESOURCE_MEM_64) ? 1 : 0;
 }
 
-static void pci_read_bases(struct pci_dev *dev, unsigned int howmany, int rom)
+static __always_inline void pci_read_bases(struct pci_dev *dev,
+					   unsigned int howmany, int rom)
 {
 	u32 rombar, stdbars[PCI_STD_NUM_BARS];
 	unsigned int pos, reg;
 	u16 orig_cmd;
 
-	BUILD_BUG_ON(howmany > PCI_STD_NUM_BARS);
+	BUILD_BUG_ON(statically_true(howmany > PCI_STD_NUM_BARS));
 
 	if (dev->non_compliant_bars)
 		return;