drm/msm/sde: Fix for loop declarations

Not all compilers support c99 or c11 mode by default, so shy away
from using mode specific features.

 drivers/gpu/drm/msm/sde/sde_hw_reg_dma_v1_color_proc.c:387:
   'for' loop initial declarations are only allowed in C99 or C11 mode
   for (u32 i = 0 ; i < hw_cfg->num_of_mixers; i++) {

Fixes: ee0bd7f3 ("drm/msm/sde: Add support for REGDMA broadcast for DSPP")
Change-Id: Ic0dedbadf1033ef4540cd93aa925d644f7f6fb10
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>