sched: walt: Fix warning introduced in sched_fork

Below warning was introduced by commit bb5b6b3e
("sched: Add snapshot of Window Assisted Load Tracking (WALT)"),
fix it.

[ 1.801550] BUG: sleeping function called from invalid context \
at kernel/mm/slab.h:421
[ 1.853289] Call trace:
[ 1.855724] dump_backtrace+0x0/0x378
[ 1.859324] show_stack+0x20/0x2c
[ 1.862996] __dump_stack+0x20/0x28
[ 1.866463] dump_stack+0x70/0x94
[ 1.870108] ___might_sleep+0x11c/0x138
[ 1.873745] __might_sleep+0x50/0x84
[ 1.877501] __kmalloc+0x80/0x350
[ 1.881073] init_new_task_load+0x7c/0x108
[ 1.884975] sched_fork+0x4c/0x230
[ 1.888606] copy_process+0x61c/0x1654
[ 1.892209] _do_fork+0x9c/0x38c
[ 1.895480] kernel_thread+0x40/0x50
[ 1.899167] kthreadd+0xfc/0x15c
[ 1.902512] ret_from_fork+0x10/0x18

Change-Id: I5d5212eae5b85d7e8924a48e4d4b5d72c9cec2aa
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>