Correct partly nested comment.

From-SVN: r3796

gcc/expr.h

@@ -204,7 +204,7 @@ enum direction {none, upward, downward};  /* Value has this type.  */
    - if the padding and mode of the type is such that a copy into a register
      would put it into the wrong part of the register.
 
-/* Which padding can't be supported depends on the byte endianness.
+   Which padding can't be supported depends on the byte endianness.
 
    A value in a register is implicitly padded at the most significant end.
    On a big-endian machine, that is the lower end in memory.