/dev/mem: allow rewinding

commit dcefafb6 ("/dev/mem: dont allow seek to last page") inadvertently
disabled rewinding on /dev/mem.

This broke x86info for example.
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
Acked-by: NWu Fengguang <fengguang.wu@intel.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/char/mem.c

@@ -710,11 +710,6 @@ static loff_t memory_lseek(struct file *file, loff_t offset, int orig)
 	switch (orig) {
 	case SEEK_CUR:
 		offset += file->f_pos;
-		if ((unsigned long long)offset <
-		    (unsigned long long)file->f_pos) {
-			ret = -EOVERFLOW;
-			break;
-		}
 	case SEEK_SET:
 		/* to avoid userland mistaking f_pos=-9 as -EBADF=-9 */
 		if ((unsigned long long)offset >= ~0xFFFULL) {