exec.c: fix setting 1-byte-long watchpoints

With commit 05068c0d 'exec.c: Relax restrictions on watchpoint length
and alignment' it's no longer possible to set 1-byte-long watchpoint
because of incorrect address range check.
Fix that by changing condition that checks for address wraparound.
Signed-off-by: NMax Filippov <jcmvbkbc@gmail.com>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Message-id: 1411016616-29879-1-git-send-email-jcmvbkbc@gmail.com
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

exec.c

@@ -595,7 +595,7 @@ int cpu_watchpoint_insert(CPUState *cpu, vaddr addr, vaddr len,
     CPUWatchpoint *wp;
 
     /* forbid ranges which are empty or run off the end of the address space */
-    if (len == 0 || (addr + len - 1) <= addr) {
+    if (len == 0 || (addr + len - 1) < addr) {
         error_report("tried to set invalid watchpoint at %"
                      VADDR_PRIx ", len=%" VADDR_PRIu, addr, len);
         return -EINVAL;