drm/amdgpu: add missing size check in amdgpu_debugfs_gprwave_read()

commit 4d75b9468021c73108b4439794d69e892b1d24e3 upstream.

Avoid a possible buffer overflow if size is larger than 4K.

Reviewed-by: Yang Wang <kevinyang.wang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit f5d873f5825b40d886d03bd2aede91d4cf002434)
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>