tpm: replace kmalloc() + memcpy() with kmemdup()

Use kmemdup rather than duplicating its implementation.

Signed-off-by: Ji-Hun Kim <ji_hun.kim@samsung.com>
Reviewed-by: James Morris <james.morris@microsoft.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkine@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkine@linux.intel.com>