irqchip: armada-370-xp: fix invalid cast of signed value into unsigned variable

The armada_370_xp_alloc_msi() function returns a signed int, which is
negative on error. However, we store the return value into an
irq_hw_number_t, which is unsigned. Therefore, we actually never test
if armada_370_xp_alloc_msi() returns an error or not, which may lead
us to use hwirq numbers of as 0xffffffe4 (when
armada_370_xp_alloc_msi() returns -ENOSPC).

This commit fixes that by storing the return value of
armada_370_xp_alloc_msi() in a signed variable.

Fixes: 31f614edb726fcc4d5aa0f2895fbdec9b04a3ca4 ('irqchip: armada-370-xp: implement MSI support')
Cc: <stable@vger.kernel.org> # v3.13+
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Link: https://lkml.kernel.org/r/1397823593-1932-2-git-send-email-thomas.petazzoni@free-electrons.com
Tested-by: Neil Greatorex <neil@fatboyfat.co.uk>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>

drivers/irqchip/irq-armada-370-xp.c

@@ -132,8 +132,7 @@ static int armada_370_xp_setup_msi_irq(struct msi_chip *chip,
 				       struct msi_desc *desc)
 {
 	struct msi_msg msg;
-	irq_hw_number_t hwirq;
-	int virq;
+	int virq, hwirq;
 
 	hwirq = armada_370_xp_alloc_msi();
 	if (hwirq < 0)