hw/xfree86: Support ACPI without APM.

On systems with ACPI but disabled APM (e.g. --disable-linux-apm)
the code does not compile due to preprocessor directives.

If APM is disabled, the final return statement is considered to
be part of ACPI's last if-statement, leading to a function which
has no final return statement at all.

I have refactored the code so ACPI and APM are independent of each
other.

Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>

hw/xfree86/os-support/linux/lnx_apm.c

@@ -138,13 +138,14 @@ xf86OSPMOpen(void)
 #ifdef HAVE_ACPI
     /* Favour ACPI over APM, but only when enabled */
 
-    if (!xf86acpiDisableFlag)
+    if (!xf86acpiDisableFlag) {
         ret = lnxACPIOpen();
-
-    if (!ret)
+        if (ret)
+            return ret;
+    }
 #endif
 #ifdef HAVE_APM
-        ret = lnxAPMOpen();
+    ret = lnxAPMOpen();
 #endif
 
     return ret;