memblock: fix memblock_phys_alloc() section mismatch error

Fix modpost Section mismatch error in memblock_phys_alloc()

[...]
WARNING: modpost: vmlinux.o(.text.unlikely+0x1dcc): Section mismatch in reference
from the function memblock_phys_alloc() to the function .init.text:memblock_phys_alloc_range()
The function memblock_phys_alloc() references
the function __init memblock_phys_alloc_range().
This is often because memblock_phys_alloc lacks a __init
annotation or the annotation of memblock_phys_alloc_range is wrong.

ERROR: modpost: Section mismatches detected.
Set CONFIG_SECTION_MISMATCH_WARN_ONLY=y to allow them.
[...]

memblock_phys_alloc() is a one-line wrapper, make it __always_inline to
avoid these section mismatches.

Reported-by: k2ci <kernel-bot@kylinos.cn>
Suggested-by: Mike Rapoport <rppt@kernel.org>
Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
[rppt: slightly massaged changelog ]
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Link: https://lore.kernel.org/r/20211217020754.2874872-1-liu.yun@linux.dev