drm/msm: fix HZ dependency of timeout

The timeout is passed as a constant which makes it HZ dependent because
jiffies are expected so it should be converted to jiffies. The actual
value is not clear from the code - my best guess is that this should be
300 milliseconds given that other timeouts are in milliseconds based on
looking at other drm drivers (e.g. exynos_drm_dsi.c:356 300ms,
tegra/dpaux.c:188 250ms) - this needs to be confirmed by someone who
knows the details of the driver.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>