vfs_read() offset is defined as loff_t, but kernel_read()
offset is only defined as unsigned long. Redefine
kernel_read() offset as loff_t.

Cc: stable@kernel.org
Signed-off-by: NMimi Zohar <zohar@us.ibm.com>
Signed-off-by: NJames Morris <jmorris@namei.org>