soc: qcom: smp2p: Don't check for NULL before ipc_log_string()

The ipc_log_string() function quietly checks for a NULL context so an
explicit check is not needed.

Change-Id: Ic0dedbada086a4daf011875cf3996c5749317307
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>