ext4: avoid unnecessary pointer dereference in ext4_mb_normalize_request

Result of EXT4_SB(ac->ac_sb) is already stored in sbi at beginning of
ext4_mb_normalize_request. Use sbi instead of EXT4_SB(ac->ac_sb) to
remove unnecessary pointer dereference.
Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Link: https://lore.kernel.org/r/20230311170949.1047958-3-shikemeng@huaweicloud.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/mballoc.c

@@ -4049,7 +4049,7 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
 		size = 8 * 1024 * 1024;
 	} else {
 		start_off = (loff_t) ac->ac_o_ex.fe_logical << bsbits;
-		size	  = (loff_t) EXT4_C2B(EXT4_SB(ac->ac_sb),
+		size	  = (loff_t) EXT4_C2B(sbi,
 					      ac->ac_o_ex.fe_len) << bsbits;
 	}
 	size = size >> bsbits;
@@ -4094,8 +4094,7 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
 			continue;
 		}
 
-		pa_end = pa->pa_lstart + EXT4_C2B(EXT4_SB(ac->ac_sb),
-						  pa->pa_len);
+		pa_end = pa->pa_lstart + EXT4_C2B(sbi, pa->pa_len);
 
 		/* PA must not overlap original request */
 		BUG_ON(!(ac->ac_o_ex.fe_logical >= pa_end ||
@@ -4128,8 +4127,7 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
 
 		spin_lock(&pa->pa_lock);
 		if (pa->pa_deleted == 0) {
-			pa_end = pa->pa_lstart + EXT4_C2B(EXT4_SB(ac->ac_sb),
-							  pa->pa_len);
+			pa_end = pa->pa_lstart + EXT4_C2B(sbi, pa->pa_len);
 			BUG_ON(!(start >= pa_end || end <= pa->pa_lstart));
 		}
 		spin_unlock(&pa->pa_lock);