nb/intel: Fix some spelling mistakes in comments and strings

Change-Id: I4a8297397d878e38516c8df19dd311c7ef19ec06
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/17478
Tested-by: build bot (Jenkins)
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/northbridge/intel/haswell/gma.c

@@ -93,7 +93,7 @@ static const struct gt_reg haswell_gt_lock[] = {
 
 /* some vga option roms are used for several chipsets but they only have one
  * PCI ID in their header. If we encounter such an option rom, we need to do
- * the mapping ourselfes
+ * the mapping ourselves
  */
 
 u32 map_oprom_vendev(u32 vendev)