ram: stm32: fix strsep failed on read only memory

strsep will change data from original memory address,
in case the memory is in non-sdram/sram place, will
run into a bug(hang at SDRAM: )

just add a temporary array to store bank_name[] to fix this
bug.

Signed-off-by: dillon min <dillon.minfei@gmail.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
diff --git a/drivers/ram/stm32_sdram.c b/drivers/ram/stm32_sdram.c
index 540ad85..3e25cc7 100644
--- a/drivers/ram/stm32_sdram.c
+++ b/drivers/ram/stm32_sdram.c
@@ -268,6 +268,7 @@
 	u32 swp_fmc;
 	ofnode bank_node;
 	char *bank_name;
+	char _bank_name[128] = {0};
 	u8 bank = 0;
 	int ret;
 
@@ -300,6 +301,8 @@
 	dev_for_each_subnode(bank_node, dev) {
 		/* extract the bank index from DT */
 		bank_name = (char *)ofnode_get_name(bank_node);
+		strlcpy(_bank_name, bank_name, sizeof(_bank_name));
+		bank_name = (char *)_bank_name;
 		strsep(&bank_name, "@");
 		if (!bank_name) {
 			pr_err("missing sdram bank index");