matrox maven: fix a broken error path

I broke an error path with d03c21ec

,
sorry about that.

The machine will crash if the i2c_attach_client() or maven_init_client()
calls fail, although nobody has yet reported this happening.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Cc: Petr Vandrovec <VANDROVE@vc.cvut.cz>
Cc: <stable@kernel.org>		[2.6.25.x, 2.6.26.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>