staging: mt7621-dma: Add braces around else branches

Add braces around else branches in conditional statements that include
branches with multiple statements. This style complies with the Linux
kernel coding style and improves consistency and readability. Issues found by
checkpatch.

Signed-off-by: Kimberly Brown <kimbrownkd@gmail.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>