msm: vidc: Add state check to allow flush command

Entry field from clock data structure gets initialized with
codec data during state transition from MSM_VIDC_CORE_INIT_DONE
to MSM_VIDC_OPEN. When flush is called before this transaction,
it calls msm_clock_data_reset where mentioned field is getting
accessed, which results in uninitialized data access. Add state
check to ensure the command is handled in right sequence.

Change-Id: Ic98221cbfe465415d89a0e2891f8af65f584f1dc
Signed-off-by: Vikash Garodia <vgarodia@codeaurora.org>