readline: Remove unneeded qemu_mallocz() check

qemu_mallocz() already checks for NULL returns, readline_init() doesn't
have to do it again.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

readline.c

@@ -467,9 +467,6 @@ ReadLineState *readline_init(Monitor *mon,
 {
     ReadLineState *rs = qemu_mallocz(sizeof(*rs));
 
-    if (!rs)
-        return NULL;
-
     rs->hist_entry = -1;
     rs->mon = mon;
     rs->completion_finder = completion_finder;