staging: erofs: fix potential overflow in erofs_grab_bio()

As Dan reported in LKP's mailing list:

https://lists.01.org/pipermail/kbuild-all/2018-August/051419.html

New smatch warnings:
drivers/staging/erofs/internal.h:446 erofs_grab_bio() warn: should 'blkaddr << (12 - 9)' be a 64 bit type?
drivers/staging/erofs/data.c:78 __erofs_get_meta_page() error: 'bio' dereferencing possible ERR_PTR()
drivers/staging/erofs/internal.h:446 erofs_grab_bio() warn: should 'blkaddr << (12 - 9)' be a 64 bit type?

Old smatch warnings:
drivers/staging/erofs/unzip_vle.c:989 z_erofs_vle_unzip() error: double unlock 'mutex:&z_pagemap_global_lock'
drivers/staging/erofs/unzip_vle.c:1318 z_erofs_vle_normalaccess_readpage() warn: should 'page->index << 12' be a 64 bit type?
drivers/staging/erofs/unzip_vle.c:1351 __z_erofs_vle_normalaccess_readpages() warn: should '()->index << 12' be a 64 bit type?

It needs to cast varable's type to sector_t before left shifting.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/erofs/internal.h

@@ -443,7 +443,7 @@ erofs_grab_bio(struct super_block *sb,
 
 	bio->bi_end_io = endio;
 	bio_set_dev(bio, sb->s_bdev);
-	bio->bi_iter.bi_sector = blkaddr << LOG_SECTORS_PER_BLOCK;
+	bio->bi_iter.bi_sector = (sector_t)blkaddr << LOG_SECTORS_PER_BLOCK;
 	return bio;
 }