msm: ipa: Fix unlock spinlock in failed condition

'Commit id I427374ef44 ("msm: ipa: Fix race condition
head_desc_list variable access")' broke unlock spinlock
in failed scenarios. Added changes to fix the issue.

Change-Id: I0f7dddfa7a583a8ebd8c1e6a610ab204726d5bc1
Acked-by: Ashok Vuyyuru <avuyyuru@qti.qualcomm.com>
Signed-off-by: Mohammed Javid <mjavid@codeaurora.org>