ANDROID: kernel: cgroup: cpuset: Add missing allocation of cpus_requested in alloc_trial_cpuset

alloc_trial_cpuset missed allocation of the alloc_trial_cpuset
field which caused it to be shared from the base cs provided.

Once update_cpumask parsed buf into cpus_requested and updated
cpus_allowed, the result were never written to cs because
cs and trialcs shared the same pointer to cpus_requested and
cpus_requested always matched to itself and no updates were
written. This caused cpus_requested to be non-empty and
cpus_allowed empty.

This issue occurs only with CONFIG_CPUMASK_OFFSTACK enabled
(e.g. via CONFIG_MAXSMP).

Bug: 134051784
Bug: 120444281
Fixes: 4803def4 ("ANDROID: cpuset: Make cpusets restore on hotplug")
Test: enable CONFIG_CPUSETS, boot and check logcat that
Test: libprocessgroup does not fail with something similar to
Test: AddTidToCgroup failed to write '2354'; fd=93: No space left on device
Signed-off-by: Roman Kiryanov <rkir@google.com>
Change-Id: I866836b5c0acfde8349c250a510ee89d8d37cb8e