drm/amdkfd: Fix missing break in switch statement

Add missing break statement in order to prevent the code from falling
through to case CHIP_NAVI10.

This bug was found thanks to the ongoing efforts to enable
-Wimplicit-fallthrough.

Fixes: 14328aa5 ("drm/amdkfd: Add navi10 support to amdkfd. (v3)")
Cc: stable@vger.kernel.org
Reviewed-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>