usb: host: xhci-msm-hsic: fix memory leak

Memory for the xhci_hcd structure stored in hcd->hcd_priv
is allocated by xhci_gen_setup() when creating the HCD,
but needs to be explicitly freed by the wrapper driver.
Call kfree on it in the HSIC remove function.

Change-Id: I35e9ea88b203daebcc4bdc00d442956e1c88d2e7
CRs-Fixed: 601546
Signed-off-by: Guang Jian Zeng <gzeng@codeaurora.org>