PCI: brcmstb: Declare 'used' as bitmap, not unsigned long

The 'used' field of 'struct brcm_msi' is used as a bitmap.  Declare it with
DECLARE_BITMAP() and adjust users accordingly.

This fixes a harmless Coverity warning about array vs singleton usage.

This bitmap can be used for either legacy or MSI interrupts, which require
a size of BRCM_INT_PCI_MSI_LEGACY_NR or BRCM_INT_PCI_MSI_NR respectively.
Add a BUILD_BUG_ON() to ensure it is large enough.

Suggested-by: Krzysztof Wilczynski <kw@linux.com>
Addresses-Coverity: "Out-of-bounds access (ARRAY_VS_SINGLETON)"
Link: https://lore.kernel.org/r/e6d9da2112aab2939d1507b90962d07bfd735b4c.1636273671.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>