msm: cvp: Fix page fault when open 16 cvp sessions

Driver created a new session but used the pointer to the session
without initialized. It happens only after driver detects more
than 16 sessions have been created. The fix is to avoid creating
new session and using of new session in case driver already runs out
of 16 max number of session limit.

Change-Id: Iaf1821a247fe4e087f1b822b9a61e9f151b0acbc
Signed-off-by: George Shen <sqiao@codeaurora.org>