IB/qib: Use memdup_user() rather than duplicating its implementation

Reuse existing functionality from memdup_user() instead of keeping
duplicate source code.

This issue was detected by using the Coccinelle software.
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/qib/qib_fs.c

@@ -328,26 +328,12 @@ static ssize_t flash_write(struct file *file, const char __user *buf,
 
 	pos = *ppos;
 
-	if (pos != 0) {
-		ret = -EINVAL;
-		goto bail;
-	}
-
-	if (count != sizeof(struct qib_flash)) {
-		ret = -EINVAL;
-		goto bail;
-	}
-
-	tmp = kmalloc(count, GFP_KERNEL);
-	if (!tmp) {
-		ret = -ENOMEM;
-		goto bail;
-	}
+	if (pos != 0 || count != sizeof(struct qib_flash))
+		return -EINVAL;
 
-	if (copy_from_user(tmp, buf, count)) {
-		ret = -EFAULT;
-		goto bail_tmp;
-	}
+	tmp = memdup_user(buf, count);
+	if (IS_ERR(tmp))
+		return PTR_ERR(tmp);
 
 	dd = private2dd(file);
 	if (qib_eeprom_write(dd, pos, tmp, count)) {
@@ -361,8 +347,6 @@ static ssize_t flash_write(struct file *file, const char __user *buf,
 
 bail_tmp:
 	kfree(tmp);
-
-bail:
 	return ret;
 }