vga_switcheroo: Constify vga_switcheroo_handler

vga_switcheroo: Constify vga_switcheroo_handler

vga_switcheroo_client_ops has always been declared const since its
introduction with 26ec685ff9d9 ("vga_switcheroo: Introduce struct
vga_switcheroo_client_ops").

Do so for vga_switcheroo_handler as well.

 drivers/gpu/drm/amd/amdgpu/amdgpu.ko:
   6 .rodata       00009888
- 19 .data         00001f00
+ 19 .data         00001ee0
 drivers/gpu/drm/nouveau/nouveau.ko:
   6 .rodata       000460b8
  17 .data         00018fe0
 drivers/gpu/drm/radeon/radeon.ko:
-  7 .rodata       00030944
+  7 .rodata       00030964
- 21 .data         0000d6a0
+ 21 .data         0000d678
 drivers/platform/x86/apple-gmux.ko:
-  7 .rodata       00000140
+  7 .rodata       00000160
- 11 .data         000000e0
+ 11 .data         000000b8

Cc: Ben Skeggs <[email protected]>
Cc: Darren Hart <[email protected]>
Cc: Alex Deucher <[email protected]>
Signed-off-by: Lukas Wunner <[email protected]>
Reviewed-by: Christian König <[email protected]>.
Signed-off-by: Daniel Vetter <[email protected]>