Staging: kpc2000: kpc_dma: Resolve cast warning and use const for file_operation

This Patch resolves unnecessary cast warning and const file_operations
reported by checkpath.pl
WARNING: unnecessary cast may hide bugs
WARNING: struct file_operations should normally be const

Signed-off-by: Vandana BN <bnvandana@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>