staging: exfat: properly support discard in clr_alloc_bitmap()

Currently the discard code in clr_alloc_bitmap() is just dead code.
Move code around so that the discard operation is properly attempted
when enabled.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Link: https://lore.kernel.org/r/20191205152913.GJ3276@xps-13Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/exfat/exfat_core.c

@@ -192,8 +192,6 @@ static s32 clr_alloc_bitmap(struct super_block *sb, u32 clu)
 
 	exfat_bitmap_clear((u8 *)p_fs->vol_amap[i]->b_data, b);
 
-	return sector_write(sb, sector, p_fs->vol_amap[i], 0);
-
 #ifdef CONFIG_EXFAT_DISCARD
 	if (opts->discard) {
 		ret = sb_issue_discard(sb, START_SECTOR(clu),
@@ -202,9 +200,13 @@ static s32 clr_alloc_bitmap(struct super_block *sb, u32 clu)
 		if (ret == -EOPNOTSUPP) {
 			pr_warn("discard not supported by device, disabling");
 			opts->discard = 0;
+		} else {
+			return ret;
 		}
 	}
 #endif /* CONFIG_EXFAT_DISCARD */
+
+	return sector_write(sb, sector, p_fs->vol_amap[i], 0);
 }
 
 static u32 test_alloc_bitmap(struct super_block *sb, u32 clu)