msm: dsi: fix dsi clock errors if ulps is disabled

Correctly setup the proper return value in case the ulps feature
is disabled. If the ulps is disabled, the dsi clock functions return
an error causing a bootup failure.

Change-Id: I2650957a5d955f66b31bc1c5f373c146efc5c23b
Signed-off-by: Siddhartha Agrawal <agrawals@codeaurora.org>