fbdev: viafb: fix typo in hw_bitblt_1 and hw_bitblt_2

[ Upstream commit bc87bb342f106a0402186bcb588fcbe945dced4b ]

There are some actions with value 'tmp' but 'dst_addr' is checked instead.
It is obvious that a copy-paste error was made here and the value
of variable 'tmp' should be checked here.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Signed-off-by: Aleksandr Burakov <a.burakov@rosalinux.ru>
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>