boot/coreboot_tables.h: Use `it is` instead of `it easy` in comment

Change-Id: I5c8a689a4923175fff1f38847b7cfbbaeeb0ea22
Signed-off-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-on: http://review.coreboot.org/7092
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins)

src/include/boot/coreboot_tables.h

@@ -77,7 +77,7 @@ struct lb_header
 /* Every entry in the boot environment list will correspond to a boot
  * info record.  Encoding both type and size.  The type is obviously
  * so you can tell what it is.  The size allows you to skip that
- * boot environment record if you don't know what it easy.  This allows
+ * boot environment record if you don't know what it is.  This allows
  * forward compatibility with records not yet defined.
  */
 struct lb_record {