drivers:staging:android:ashmem: Changing return type from int to loff_t

Changing return type from int to loff_t. Actual return type of the
function (vfs_llseek) is loff_t (long long). Here due to implicit
converion from long long to int, result will be implementation defined.

Signed-off-by: Rohit Kumar <rohit12techie@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>