matroxfb: constify local structures

For structure types defined in the same file or local header files, find
top-level static structure declarations that have the following
properties:
1. Never reassigned.
2. Address never taken
3. Not passed to a top-level macro call
4. No pointer or array-typed field passed to a function or stored in a
variable.
Declare structures having all of these properties as const.

Done using Coccinelle.
Based on a suggestion by Joe Perches <[e-mail]>.

Signed-off-by: Julia Lawall <[e-mail]>
Signed-off-by: Tomi Valkeinen <[e-mail]>

drivers/video/fbdev/matrox/matroxfb_g450.c

···
 		0x00,	/* 3E written multiple times */
 		0x00,	/* 3F not written */
 	} };
-	static struct mavenregs ntscregs = { {
+	static const struct mavenregs ntscregs = { {
 		0x21, 0xF0, 0x7C, 0x1F,	/* 00: chroma subcarrier */
 		0x00,
 		0x00,	/* test */