UPSTREAM: erofs: fold in z_erofs_decompress()

No need this helper since it's just a simple wrapper for decompress
method and only one caller.  So, let's fold in directly instead.

Signed-off-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230426084449.12781-1-zbestahu@gmail.com


Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

Bug: 318378021
(cherry picked from commit 597e2953)
Change-Id: I849360f088016cf97542858e8a5a9cee671a2f61
Signed-off-by: Sandeep Dhavale <dhavale@google.com>