drm/i915/gvt: remove redundant -Wall

This flag is already set in the top level Makefile of the kernel.

Also, by having set CONFIG_DRM_I915_GVT, thereby appending -Wall to
ccflags, you undo all the -Wno-* cflags previously set in the Make
variable KBUILD_CFLAGS.

For example:

cc foo.c -Wall -Wno-format -Wall

resets -Wformat.
Signed-off-by: Nick Desaulniers <nick.desaulniers@gmail.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

drivers/gpu/drm/i915/gvt/Makefile

@@ -3,6 +3,6 @@ GVT_SOURCE := gvt.o aperture_gm.o handlers.o vgpu.o trace_points.o firmware.o \
 	interrupt.o gtt.o cfg_space.o opregion.o mmio.o display.o edid.o \
 	execlist.o scheduler.o sched_policy.o render.o cmd_parser.o
 
-ccflags-y				+= -I$(src) -I$(src)/$(GVT_DIR) -Wall
+ccflags-y				+= -I$(src) -I$(src)/$(GVT_DIR)
 i915-y					+= $(addprefix $(GVT_DIR)/, $(GVT_SOURCE))
 obj-$(CONFIG_DRM_I915_GVT_KVMGT)	+= $(GVT_DIR)/kvmgt.o