drm/amd/display/amdgpu_dm: remove duplicate included header files

soc15_common.h is included more than once.
Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Xu Panda <xu.panda@zte.com.cn>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -98,8 +98,6 @@
 #include "soc15_common.h"
 #include "vega10_ip_offset.h"
 
-#include "soc15_common.h"
-
 #include "gc/gc_11_0_0_offset.h"
 #include "gc/gc_11_0_0_sh_mask.h"