msm: mdss: do not fail DSI probe if clk_get fails for MMSS AHB clock

On 8916, there is no support for MMSS MISC AHB clock. Hence, if clk_get
fails for this clock, do not fail DSI probe since this is expected for
this target.

Change-Id: Ifaed8588d88f1daeb07ad4392592c12abb982001
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>