drivers/video/matrox/matroxfb_maven.c: fix unsigned return type

The function has an unsigned return type, but returns a negative constant
to indicate an error condition.  The result of calling the function is
only tested by comparison to 0, and thus unsigned is not needed and can be
dropped from the return type.

A sematic match that finds this problem is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@exists@
identifier f;
constant C;
@@

 unsigned f(...)
 { <+...
*  return -C;
 ...+> }
// </smpl>
Signed-off-by: NJulia Lawall <julia@diku.dk>
Cc: Petr Vandrovec <vandrove@vc.cvut.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/video/matrox/matroxfb_maven.c

@@ -280,7 +280,7 @@ static int matroxfb_PLL_mavenclock(const struct matrox_pll_features2* pll,
 	return fxtal * (*feed) / (*in) * ctl->den;
 }
 
-static unsigned int matroxfb_mavenclock(const struct matrox_pll_ctl* ctl,
+static int matroxfb_mavenclock(const struct matrox_pll_ctl *ctl,
 		unsigned int htotal, unsigned int vtotal,
 		unsigned int* in, unsigned int* feed, unsigned int* post,
 		unsigned int* htotal2) {