mm: cma: Reduce dmesg spam

CONFIG_CMA_DEBUG was #defining DEBUG, which has the side effect of
changing the behavior of pr_debug statements to always print into
the dmesg log, as opposed to printing only if they are enabled via
dynamic debug.

Log etiquette indicates that messages should only be printed for
error conditions.

Change-Id: I5eebc1060618a3abc87a7f85ae770505c991c017
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>