msm: kgsl: Fix uninitialized variable in adreno_ringbuffer_probe()

To avoid possibility of using 'status' variable uninitialized,
safely initializing it to -ENOMEM.

Change-Id: I02b05e78b8d7878dc9bc60d40dc91217adeff364
Signed-off-by: Archana Sriram <apsrir@codeaurora.org>