msm: kgsl: Fix integer overflow in kgsl_ioctl_gpu_aux_command ioctl

In kgsl_ioctl_gpu_aux_command, if the number of generic objects passed is
UINT_MAX - 1 along with a syncpoint object, the count variable will be
incremented twice: once for timestamp sync object and another for aux
command syncpoint object resulting in count value as 0. Fix this by
allowing maximum of UINT_MAX - 2 generic objects.

Change-Id: Ief8c8da9b147e4b45b1f53d42473b772cedf77a8
Signed-off-by: Kamal Agrawal <kamaagra@codeaurora.org>