remoteproc: qcom: Add missing slab.h

remoteproc: qcom: Add missing slab.h

drivers/remoteproc/qcom_common.c: In function 'qcom_ssr_get_subsys':
drivers/remoteproc/qcom_common.c:210:9: error: implicit declaration of function 'kzalloc'; did you mean 'vzalloc'?
[-Werror=implicit-function-declaration]
  info = kzalloc(sizeof(*info), GFP_KERNEL);
         ^~~~~~~
         vzalloc

kzalloc() is declared in linux/slab.h, add include to fix build issue.

Tested-by: Alex Elder <elder@linaro.org>
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Link: https://lore.kernel.org/r/20200713020003.134039-1-wangkefeng.wang@huawei.com
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>