iommu/msm: Make msm_iommu_lock static

iommu/msm: Make msm_iommu_lock static

Fix the following sparse warning:

drivers/iommu/msm_iommu.c:37:1: warning: symbol 'msm_iommu_lock' was not declared.

The msm_iommu_lock has only call site within msm_iommu.c
It should be static

Fixes: 0720d1f052dc ("msm: Add MSM IOMMU support")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Samuel Zou <zou_wei@huawei.com>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/1589249839-105820-1-git-send-email-zou_wei@huawei.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>