drm/i915: fix naming of fixed_16_16 wrapper.

fixed_16_16_div_round_up(_u64), wrapper for fixed_16_16 division
operation don't really round_up the result. Wrapper round_up only the
fraction part of the result to make it 16-bit.
This patch eliminates round_up keyword from the wrapper.

Later patch will introduce the new wrapper to do rounding-off the result
and give unt32_t output to cleanup mix use of fixed_16_16_t & uint32_t
variables.

Signed-off-by: Mahesh Kumar <mahesh1.kumar@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170517115831.13830-2-mahesh1.kumar@intel.com