cirrus: fix blit address mask handling

Apply the cirrus_addr_mask to cirrus_blt_dstaddr and cirrus_blt_srcaddr
right after assigning them, in cirrus_bitblt_start(), instead of having
this all over the place in the cirrus code, and missing a few places.

Reported-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 1485338996-17095-1-git-send-email-kraxel@redhat.com
(cherry picked from commit 60cd23e8)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>