staging: fbtft: replace ternary operator with min macro

Use macro min() to get the minimum of two values for
brevity and readability.

Found using Coccinelle:
@@ type T; T x; T y; @@
(
- x < y ? x : y
+ min(x,y)
|
- x > y ? x : y
+ max(x,y)
)

Signed-off-by: Alison Schofield <amsfield22@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>