Staging: mt7621_dma: Prefer unsigned int over just unsigned

Replace 'unsigned' with 'unsigned int' to be specific with data type.
Issue found with checkpatch.pl

Signed-off-by: Bhanusree Pola <bhanusreemahesh@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>