mm/gup_test.c: mark gup_test_init as __init function

gup_test_init() is only called during initialization, mark it as __init to
save some memory.

Link: https://lkml.kernel.org/r/20201103081016.16532-1-song.bao.hua@hisilicon.comSigned-off-by: Barry Song <song.bao.hua@hisilicon.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/gup_test.c

@@ -236,7 +236,7 @@ static const struct file_operations gup_test_fops = {
 	.unlocked_ioctl = gup_test_ioctl,
 };
 
-static int gup_test_init(void)
+static int __init gup_test_init(void)
 {
 	debugfs_create_file_unsafe("gup_test", 0600, NULL, NULL,
 				   &gup_test_fops);