[Build] Add missing <errno.h> include for errno

[nuclearcat]

mos_query_device_type() uses errno, but mos_bufmgr_api.h does not include its declaring header.

With Clang 22 and libc++ 22, enabling -D_LIBCPP_REMOVE_TRANSITIVE_INCLUDES=1 makes both hwinfo_linux.cpp and mos_auxtable_mgr.cpp fail with:

mos_bufmgr_api.h:434:68: error: use of undeclared identifier 'errno'

Include <errno.h> directly in the header that uses it, alongside the existing C headers. No functional change.

Validation against master 2ad1459d2f80af7b034499238c0022ff00652b70:

• Both translation units pass syntax checks with default libc++ includes, fail with transitive includes disabled, and pass after this change without forced includes.
• Both compile to object files with transitive includes disabled after the change.
• git diff --check passes.

These were targeted checks with ChromeOS Clang/libc++ 22 and Ubuntu host C headers; no full driver build or hardware tests were run.

This also covers the <errno.h> hunk in ChromeOS CL 7964643.

AI assistance used for investigation, validation, and preparing this PR.