drm/amd/amdgpu/gfx_v10_0: Make local function 'gfx_v10_0_rlc_stop()' static

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c:5008:6: warning: no previous prototype for ‘gfx_v10_0_rlc_stop’ [-Wmissing-prototypes]

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c

@@ -5014,7 +5014,7 @@ static int gfx_v10_0_init_csb(struct amdgpu_device *adev)
 	return 0;
 }
 
-void gfx_v10_0_rlc_stop(struct amdgpu_device *adev)
+static void gfx_v10_0_rlc_stop(struct amdgpu_device *adev)
 {
 	u32 tmp = RREG32_SOC15(GC, 0, mmRLC_CNTL);