ext4: correct start of used group pa for debug in ext4_mb_use_group_pa

As we don't correct pa_lstart here, so there is no need to subtract
pa_lstart with consumed len.
Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://lore.kernel.org/r/20230303172120.3800725-6-shikemeng@huaweicloud.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/mballoc.c

@@ -4323,7 +4323,7 @@ static void ext4_mb_use_group_pa(struct ext4_allocation_context *ac,
 	 * Other CPUs are prevented from allocating from this pa by lg_mutex
 	 */
 	mb_debug(ac->ac_sb, "use %u/%u from group pa %p\n",
-		 pa->pa_lstart-len, len, pa);
+		 pa->pa_lstart, len, pa);
 }
 
 /*