sched: core: fix kmalloc error during spinlock

The patch, pa/1759800, incorrectly used the 'kmalloc(sizeof(...),
GFP_KERNEL)' during spinlock section.

Bug: 173167141
Test: enable CONFIG_PANIC_ON_SCHED_BUG, boot to home
Change-Id: Ifa1619c9b0d3a784a46bc344ec24a4cefd27c91b
Signed-off-by: Jimmy Shiu <jimmyshiu@google.com>