The current implementation of the DMA40's local MAX() macro evaluates
its arguments more times than is necessary and it not type checked.
This patch strips replaces it with a new, more efficient constant.

Cc: Dan Williams <djbw@fb.com>
Cc: Per Forlin <per.forlin@stericsson.com>
Cc: Rabin Vincent <rabin@rab.in>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Reported-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>