firmware: Initialize firmware_buf list when we create a new firmware buf

In the case where we use FW_OPT_NOCACHE, the firmware_buf list will have
NULL entries resulting in NULL pointer dereferences when we enter an
error condition.

[<ffffff8ad75fe59c>] list_del+0x14
[<ffffff8ad78efe6c>] __fw_free_buf+0x38
[<ffffff8ad78effa8>] fw_free_buf+0x5c
[<ffffff8ad78f0024>] release_firmware+0x70
[<ffffff8ad78f0c80>] _request_firmware+0x60
[<ffffff8ad78f18e0>] request_firmware_into_buf+0x4c

Change-Id: I0ca6c44c19317ccb55aa2ec7259402a67a90ab79
Signed-off-by: Kyle Yan <kyan@codeaurora.org>
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>