checkpatch: There is no qemu_strtod()

Maybe there should be; but until there is, we should not flag
strtod() calls as something to replaced with qemu_strtod().

We also lack qemu_strtof() and qemu_strtold(), but as no one
has been using strtof() or strtold(), it's not worth complicating
the regex for them.

(Ironically, I had to use 'git commit -n' since checkpatch uses
TAB indents, in violation of its own recommendations.)

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1465526889-8339-3-git-send-email-eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>