Staging: mt7621-dma: Remove braces around single if statement

Fix following checkpatch.pl warning by removing unnecessary braces:
WARNING: braces {} are not necessary for single statement blocks

Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>