mtd: pmcmsp: use kstrndup instead of kmalloc+strncpy

kernelci.org reports a warning for this driver, as it copies a local
variable into a 'const char *' string:

    drivers/mtd/maps/pmcmsp-flash.c:149:30: warning: passing argument 1 of 'strncpy' discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]

Using kstrndup() simplifies the code and avoids the warning.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/maps/pmcmsp-flash.c

@@ -139,15 +139,13 @@ static int __init init_msp_flash(void)
 		}
 
 		msp_maps[i].bankwidth = 1;
-		msp_maps[i].name = kmalloc(7, GFP_KERNEL);
+		msp_maps[i].name = kstrndup(flash_name, 7, GFP_KERNEL);
 		if (!msp_maps[i].name) {
 			iounmap(msp_maps[i].virt);
 			kfree(msp_parts[i]);
 			goto cleanup_loop;
 		}
 
-		msp_maps[i].name = strncpy(msp_maps[i].name, flash_name, 7);
-
 		for (j = 0; j < pcnt; j++) {
 			part_name[5] = '0' + i;
 			part_name[7] = '0' + j;