ART: set growth limit to heap size when it is larger.

The growth limit set by -XX:HeapGrowthLimit could be larger than the
heap size, which cause ART crash. set growth limit to heap size if it
is larger.

Change-Id: I9dffa9ce39a86cf347fbd7a2f7ab12642aea5c60
Signed-off-by: Zang Lin <lin.zang@intel.com>