s390: avoid always-true comparison in s390_pci_generate_fid()

Coverity points out that the comparison "fid <= ZPCI_MAX_FID"
in s390_pci_generate_fid() is always true (because fid
is 32 bits and ZPCI_MAX_FID is 0xffffffff). This isn't a
bug because the real loop termination condition is
expressed later via an "if (...) break;" inside the loop,
but it is a bit odd. Rephrase the loop to avoid the
unnecessary duplicate-but-never-true conditional.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

hw/s390x/s390-pci-bus.c

@@ -809,17 +809,11 @@ static uint32_t s390_pci_generate_fid(Error **errp)
 {
     uint32_t fid = 0;
 
-    while (fid <= ZPCI_MAX_FID) {
+    do {
         if (!s390_pci_find_dev_by_fid(fid)) {
             return fid;
         }
-
-        if (fid == ZPCI_MAX_FID) {
-            break;
-        }
-
-        fid++;
-    }
+    } while (fid++ != ZPCI_MAX_FID);
 
     error_setg(errp, "no free fid could be found");
     return 0;