msm: vidc: Fix check to see if ocmem buffer is allocated

The driver was skipping voting for ocmem bandwidth when ocmem was
allocated.  The intention is to skip the vote if it is _not_ allocated.

Hence, fix the incorrect non-NULL check.

Change-Id: Ifddd1d2fa55ea1d359ef6931b597d1abc62b06fd
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>