ACPI: fix false-positive -Wuninitialized warning

clang gets confused by an uninitialized variable in what looks
to it like a never executed code path:

arch/x86/kernel/acpi/boot.c:618:13: error: variable 'polarity' is uninitialized when used here [-Werror,-Wuninitialized]
        polarity = polarity ? ACPI_ACTIVE_LOW : ACPI_ACTIVE_HIGH;
                   ^~~~~~~~
arch/x86/kernel/acpi/boot.c:606:32: note: initialize the variable 'polarity' to silence this warning
        int rc, irq, trigger, polarity;
                                      ^
                                       = 0
arch/x86/kernel/acpi/boot.c:617:12: error: variable 'trigger' is uninitialized when used here [-Werror,-Wuninitialized]
        trigger = trigger ? ACPI_LEVEL_SENSITIVE : ACPI_EDGE_SENSITIVE;
                  ^~~~~~~
arch/x86/kernel/acpi/boot.c:606:22: note: initialize the variable 'trigger' to silence this warning
        int rc, irq, trigger, polarity;
                            ^
                             = 0

This is unfortunately a design decision in clang and won't be fixed.

Changing the acpi_get_override_irq() macro to an inline function
reliably avoids the issue.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

include/linux/acpi.h

@@ -324,7 +324,10 @@ struct irq_domain *acpi_irq_create_hierarchy(unsigned int flags,
 #ifdef CONFIG_X86_IO_APIC
 extern int acpi_get_override_irq(u32 gsi, int *trigger, int *polarity);
 #else
-#define acpi_get_override_irq(gsi, trigger, polarity) (-1)
+static inline int acpi_get_override_irq(u32 gsi, int *trigger, int *polarity)
+{
+	return -1;
+}
 #endif
 /*
  * This function undoes the effect of one call to acpi_register_gsi().