matroxfb: get rid of unneeded macro MINFO_FROM

With multihead support always enabled, macros MINFO_FROM and
MINFO_FROM_INFO are no longer needed and make the code harder to read.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Petr Vandrovec <vandrove@vc.cvut.cz>
Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>