spitz tosa: Simplify "drive is suitable for microdrive" test

spitz tosa: Simplify "drive is suitable for microdrive" test

We try the drive defined with -drive if=ide,index=0 (or equivalent
sugar).  We use it only if (dinfo && bdrv_is_inserted(dinfo->bdrv) &&
!bdrv_is_removable(dinfo->bdrv)).  This is a convoluted way to test
for "drive media can't be removed".

The only way to create such a drive with -drive if=ide is media=cdrom.
And that sets dinfo->media_cd, so just test that.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>