drm/mgag200: Rename mgag200_i2c.c to mgag200_ddc.c

Rename the source file according to its content. No functional
changes.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240513125620.6337-8-tzimmermann@suse.de

drivers/gpu/drm/mgag200/Makefile

 # SPDX-License-Identifier: GPL-2.0-only
 mgag200-y := \
 	mgag200_bmc.o \
+	mgag200_ddc.o \
 	mgag200_drv.o \
 	mgag200_g200.o \
 	mgag200_g200eh.o \
@@ -10,7 +11,6 @@ mgag200-y := \
 	mgag200_g200ew3.o \
 	mgag200_g200se.o \
 	mgag200_g200wb.o \
-	mgag200_i2c.o \
 	mgag200_mode.o
 
 obj-$(CONFIG_DRM_MGAG200) += mgag200.o