/proc/kcore: fix seeking

Commit 34aacb2920 ("procfs: Use generic_file_llseek in /proc/kcore") broke
seeking on /proc/kcore.  This changes it back to use default_llseek in
order to restore the original behavior.

The problem with generic_file_llseek is that it only allows seeks up to
inode->i_sb->s_maxbytes, which is 2GB-1 on procfs, where the memory file
offset values in the /proc/kcore PT_LOAD segments may exceed or start
beyond that offset value.

A similar revert was made for /proc/vmcore.

Signed-off-by: Dave Anderson <anderson@redhat.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/kcore.c

@@ -558,7 +558,7 @@ static int open_kcore(struct inode *inode, struct file *filp)
 static const struct file_operations proc_kcore_operations = {
 	.read		= read_kcore,
 	.open		= open_kcore,
-	.llseek		= generic_file_llseek,
+	.llseek		= default_llseek,
 };
 
 #ifdef CONFIG_MEMORY_HOTPLUG