Fix bug of printing error msg in kern log

Stop using vm_operations_struct->fault to handle memory mapping from
kernel to userspace, use dev->mmap directly (in function logger_mmap).

In the previous version, kernel map page to userspace via page fault
path, but doesn't register this page to userspace paging structure.
So something may be wrong when calling munmap.

Signed-off-by: Arthur Chunqi Li <yzt356@gmail.com>