scsi: ufs: fix compiling error when FTRACE disabled

We should not define __ufshcd_cmd_log when !CONFIG_TRACEPOINTS.
It will not be called.

Change-Id: I1c0665c7920630159990c1e81856ea45b0f5d32c
Signed-off-by: Zhenhua Huang <zhenhuah@codeaurora.org>