hv_netvsc: Fix potential dereference of NULL pointer

The return value of netvsc_devinfo_get()
needs to be checked to avoid use of NULL
pointer in case of an allocation failure.

Fixes: 0efeea5f ("hv_netvsc: Add the support of hibernation")
Signed-off-by: Yongzhi Liu <lyz_cs@pku.edu.cn>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Link: https://lore.kernel.org/r/1652962188-129281-1-git-send-email-lyz_cs@pku.edu.cn


Signed-off-by: Jakub Kicinski <kuba@kernel.org>