tridentfb: register should be left in non-locked state

Remove locking registers after they are unlocked during switch to/from MMIO
mode.  This fixes regression on the Blade3D (Trident 9880) caused by the
previous patch (probe fixes).

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>