twl6030 battery: assume default capacity if not specified

If platform data does not pass down the nominal battery capacity,
then assume a sane default value.

Change-Id: Icba698fb0d2f14cc778740734ed8f2c573e67f0d
Signed-off-by: Sivakumar Pothireddy <sivakumar.pothireddy@ti.com>
Signed-off-by: Anand Gadiyar <gadiyar@ti.com>