msm: ocmem: Improve error handling during allocation of ocmem memory

The unsigned long address variable cannot be used to return errors
from the allocation function because it does not correctly report
signed errors.

Update the allocate_head() and allocate_tail() functions to
seperate the return value from the offset address.

Change-Id: I1258623c15d241649cd1ce32230928bbbe5d35ad
Signed-off-by: Neeti Desai <neetid@codeaurora.org>