Add formating directive line in function `drm_gpuvm_sm_map_exec_lock()`
comment to clear warning messages shown bellow that appears generating
documentation `make htmldocs`.
Warning: ./drivers/gpu/drm/drm_gpuvm.c:2444: Unexpected indentation.
Warning: ./drivers/gpu/drm/drm_gpuvm.c:2446: Block quote ends without a blank line; unexpected unindent.
Warning: ./drivers/gpu/drm/drm_gpuvm.c:2450: Definition list ends without a blank line; unexpected unindent.
Warning: ./drivers/gpu/drm/drm_gpuvm.c:2451: Definition list ends without a blank line; unexpected unindent.
Warning: ./drivers/gpu/drm/drm_gpuvm.c:2455: Unexpected indentation.
Warning: ./drivers/gpu/drm/drm_gpuvm.c:2456: Definition list ends without a blank line; unexpected unindent.
Warning: ./drivers/gpu/drm/drm_gpuvm.c:2457: Definition list ends without a blank line; unexpected unindent.
Warning: ./drivers/gpu/drm/drm_gpuvm.c:2458: Definition list ends without a blank line; unexpected unindent.
Fixes: 471920ce25d5 ("drm/gpuvm: Add locking helpers")
Signed-off-by: Javier Garcia <rampxxxx@xxxxxxxxx>