greybus: loopback: remove checkpatch error causing macro

checkpatch.pl is choking on a later change to dev_stats_attrs, where
checkpatch expects to see the values encapsulated in curly brackets.
Encapsulating in curly brackets will cause a compiler error. To resolve the
dichotomy this patch drops the macros and adds the arrary declarations
directly.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>