Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
diff --git a/include/video/kyro.h b/include/video/kyro.h
index dba7de2..c563968 100644
--- a/include/video/kyro.h
+++ b/include/video/kyro.h
@@ -32,7 +32,7 @@
 	u32 PIXCLK;	/* Pixel Clock       */
 	u32 HCLK;	/* Hor Clock         */
 
-	/* Usefull to hold depth here for Linux */
+	/* Useful to hold depth here for Linux */
 	u8 PIXDEPTH;
 
 #ifdef CONFIG_MTRR