s390/mm: correct comment about segment table entries

The comment describing the bit encoding for segment table entries
is incorrect in regard to the read and write bits. The segment
read bit is 0x0002 and write is 0x0001, not the other way around.
Reported-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/pgtable.h

@@ -298,15 +298,15 @@ static inline int is_module_addr(void *addr)
 
 /*
  * Segment table entry encoding (R = read-only, I = invalid, y = young bit):
- *				dy..R...I...wr
+ *				dy..R...I...rw
  * prot-none, clean, old	00..1...1...00
  * prot-none, clean, young	01..1...1...00
  * prot-none, dirty, old	10..1...1...00
  * prot-none, dirty, young	11..1...1...00
- * read-only, clean, old	00..1...1...01
- * read-only, clean, young	01..1...0...01
- * read-only, dirty, old	10..1...1...01
- * read-only, dirty, young	11..1...0...01
+ * read-only, clean, old	00..1...1...10
+ * read-only, clean, young	01..1...0...10
+ * read-only, dirty, old	10..1...1...10
+ * read-only, dirty, young	11..1...0...10
  * read-write, clean, old	00..1...1...11
  * read-write, clean, young	01..1...0...11
  * read-write, dirty, old	10..0...1...11