media: ipu3: drop an unused variable

Fix this clang Werror with W=1:

	drivers/staging/media/ipu3/ipu3-css-params.c:774:8: error: variable 'pin_scale' set but not used [-Werror,-Wunused-but-set-variable]
	                        int pin_scale = 0;
	                            ^

Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>