GCC4.6: Squash warnings in ipu_disp.c

ipu_disp.c: In function ‘ipu_disp_set_global_alpha’:
ipu_disp.c:1237:11: warning: variable ‘flow’ set but not used
[-Wunused-but-set-variable]
ipu_disp.c: In function ‘ipu_disp_set_color_key’:
ipu_disp.c:1302:16: warning: variable ‘flow’ set but not used
[-Wunused-but-set-variable]

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Cc: Stefano Babic <sbabic@denx.de>