staging: fbtft: Avoid potential precedence issues

Put parentheses around uses of macro parameters to avoid possible
precedence issues. Problem detected by checkpatch.

Signed-off-by: Deepak R Varma <mh12gx2825@gmail.com>
Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
Link: https://lore.kernel.org/r/5c8520a5c3da453460608deee9a25232d52f4513.1584314604.git.mh12gx2825@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>