mtd: rawnand: qcom: Fix build issue on x86 architecture

Fix a buffer overflow issue in qcom_clear_bam_transaction by using
struct_group to group related fields and avoid FORTIFY_SOURCE warnings.

On x86 architecture, the following error occurs due to warnings being
treated as errors:

In function ‘fortify_memset_chk’,
    inlined from ‘qcom_clear_bam_transaction’ at
drivers/mtd/nand/qpic_common.c:88:2:
./include/linux/fortify-string.h:480:25: error: call to ‘__write_overflow_field’
declared with attribute warning: detected write beyond size of field
(1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
  480 |                         __write_overflow_field(p_size_field, size);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  LD [M]  drivers/mtd/nand/nandcore.o
  CC [M]  drivers/w1/masters/mxc_w1.o
cc1: all warnings being treated as errors

This patch addresses the issue by grouping the related fields in
struct bam_transaction using struct_group and updating the memset call
accordingly.

Fixes: 8c52932 ("mtd: rawnand: qcom: cleanup qcom_nandc driver")
Signed-off-by: Md Sadre Alam <quic_mdalam@quicinc.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

Author: Md Sadre Alam

drivers/mtd/nand/qpic_common.c

@@ -85,7 +85,7 @@ void qcom_clear_bam_transaction(struct qcom_nand_controller *nandc)
 	if (!nandc->props->supports_bam)
 		return;
 
-	memset(&bam_txn->bam_ce_pos, 0, sizeof(u32) * 8);
+	memset(&bam_txn->bam_positions, 0, sizeof(bam_txn->bam_positions));
 	bam_txn->last_data_desc = NULL;
 
 	sg_init_table(bam_txn->cmd_sgl, nandc->max_cwperpage *

include/linux/mtd/nand-qpic-common.h

@@ -254,14 +254,17 @@ struct bam_transaction {
 	struct dma_async_tx_descriptor *last_data_desc;
 	struct dma_async_tx_descriptor *last_cmd_desc;
 	struct completion txn_done;
-	u32 bam_ce_pos;
-	u32 bam_ce_start;
-	u32 cmd_sgl_pos;
-	u32 cmd_sgl_start;
-	u32 tx_sgl_pos;
-	u32 tx_sgl_start;
-	u32 rx_sgl_pos;
-	u32 rx_sgl_start;
+	struct_group(bam_positions,
+		u32 bam_ce_pos;
+		u32 bam_ce_start;
+		u32 cmd_sgl_pos;
+		u32 cmd_sgl_start;
+		u32 tx_sgl_pos;
+		u32 tx_sgl_start;
+		u32 rx_sgl_pos;
+		u32 rx_sgl_start;
+
+	);
 };
 
 /*