Remove MAX when initializing arc_c_max

The MAX when initializing arc_c_max doesn't make any sense because
it hasn't been set anywhere before. Though, arc_c_max should be
implicitly set to zero when initializing arc_stats, so the MAX
doesn't make any difference.

The MAX was mistakenly left if place when the Illumos default
values were changed for Linux.

Signed-off-by: david.chen <tuxoko@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1941