staging: fbtft: remove unnecessary parantheses around assignment

Parentheses are not needed around the right hand side of an assignment.
This patch is done using Coccinelle:

@@
expression a, b;
@@

b =
-(
a
-)

Signed-off-by: Aastha Gupta <aastha.gupta4104@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>