staging: mt7621-mmc: Use BIT macro instead of explicit shifting in dbg.h

Replace explicit shifting with BIT macro in dbg.h.
Issue found by checkpatch.

Signed-off-by: Nishad Kamdar <nishadkamdar@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>