msm: ipa: bug fix for memory leak in add_mbim_hdr

bug fix for memory leak in teth_bridge.c, which was found in add_mbim_hdr.

Change-Id: I940e5d81e7e991aadf4c2b0bbb342cbbd23b9891
CRs-Fixed: 556881
Acked-by: Yaniv Hasbani <yhasbani@qti.qualcomm.com>
Signed-off-by: Gidon Studinski <gidons@codeaurora.org>