soc: qcom: hwkm: check key size before unwrap

Make sure key size is what is expected by command packet
for KEY_UNWRAP_IMPORT in order to not overflow the buffer
and corrupt the stack.

Change-Id: Iba1d6bb3bf5efc4f4e64dafce0fbb65bb6f7b8c6
Signed-off-by: Gaurav Kashyap <gaurkash@codeaurora.org>