tridentfb: resource management fixes in probe function

Correct error paths in probe function.

The probe function enables mmio mode so it important to disable the mmio
mode before exiting the probe function.  Otherwise, the console is left in
unusable state (garbled fonts at least, lock up at worst).

[akpm@linux-foundation.org: cleanups]
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>