iommu/msm: Add a check for the return of kzalloc()

kzalloc() is a memory allocation function which can return NULL when
some internal memory errors happen. So it is better to check it to
prevent potential wrong memory access.

Besides, to propagate the error to the caller, the type of
insert_iommu_master() is changed to `int`. Several instructions related
to it are also updated.

Signed-off-by: Xiaoke Wang <xkernel.wang@foxmail.com>
Link: https://lore.kernel.org/r/tencent_EDB94B1C7E14B4E1974A66FF4D2029CC6D08@qq.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>