soc: qcom: glink_pkt: Remove BUG_ON in glink_pkt_write

BUG_ON is called when error is returned from copy_from_user and
copy_to_user apis.

BUG_ON is removed and appropriate error value is returned after cleanup.

CRs-Fixed: 1102504
Change-Id: Ia995e60b8d8d335239be0a35876d1becfd9a0f3c
Signed-off-by: Dhoat Harpal <hdhoat@codeaurora.org>