Problem fixed. Environment was set incorrectly.
Before Fixed
args_ramfs=setenv bootargs ${bootargs} earlyprintk rdinit=/sbin/init rw root=/dev/ram0 initrd=0x802000000,9M
After fixed
args_ramfs=setenv bootargs earlyprintk rdinit=/sbin/init rw root=/dev/ram0 initrd=0x802000000,80M
