[SPARC]: Eliminate local MIN/MAX macros in drivers/sbus/char/aurora.c

From: Christophe Lucas <clucas@rotomalug.org>

min/max macros from kernel.h are safe, a lot of handcrafted MIN/MAX are
not.

Signed-off-by: Christophe Lucas <clucas@rotomalug.org>
Signed-off-by: Domen Puncer <domen@coderock.org>