Fix empty if statement

Add noop to fix:
/system/bin/memcgv2_activation_depth.sh[76]: syntax error: unexpected 'elif'

Bug: 393588812
Fixes: a88db824 ("Don't reboot for memcg MaxActivationDepth reduction")
Test: /system/bin/memcgv2_activation_depth.sh 3
Test: find /sys/fs/cgroup -name cgroup.controllers -exec grep -q memory {} \; -print
Test: /system/bin/memcgv2_activation_depth.sh 0 (no reboot)
Ignore-AOSP-First: 25Q2 Beta Experiment only go/android-memcgv2-exp
Change-Id: Ia219f7f30c49911dfc347511740db37362f54dbf