um: Fix comment typo

The double `in' is duplicated in line 172, remove one.

Signed-off-by: Jason Wang <[e-mail]>
Signed-off-by: Richard Weinberger <[e-mail]>

arch/um/kernel/physmem.c

···
 );
 
 /*
- * This list is constructed in parse_iomem and addresses filled in in
+ * This list is constructed in parse_iomem and addresses filled in
  * setup_iomem, both of which run during early boot.  Afterwards, it's
  * unchanged.
  */