Fix bad command length calculation

SET_LAYER_PER_FRAME_METADATA_BLOBS command length
was calculated wrong. With wrong length
it's impossible to read current and any next commands right.

Test: manual
Bug: 144367999

Change-Id: I09a23bbf507996972ce7de0634f8866bbb13152a
Signed-off-by: o.v.yevtushenko <o.v.yevtushenko@globallogic.com>