switch a bunch of places to mnt_want_write_file()

it's both faster (in case when file has been opened for write) and cleaner.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/ext3/ioctl.c b/fs/ext3/ioctl.c
index ba1b54e..a02863a 100644
--- a/fs/ext3/ioctl.c
+++ b/fs/ext3/ioctl.c
@@ -44,7 +44,7 @@
 		if (get_user(flags, (int __user *) arg))
 			return -EFAULT;
 
-		err = mnt_want_write(filp->f_path.mnt);
+		err = mnt_want_write_file(filp);
 		if (err)
 			return err;
 
@@ -126,7 +126,7 @@
 		if (!inode_owner_or_capable(inode))
 			return -EPERM;
 
-		err = mnt_want_write(filp->f_path.mnt);
+		err = mnt_want_write_file(filp);
 		if (err)
 			return err;
 		if (get_user(generation, (int __user *) arg)) {
@@ -164,7 +164,7 @@
 		if (!test_opt(inode->i_sb, RESERVATION) ||!S_ISREG(inode->i_mode))
 			return -ENOTTY;
 
-		err = mnt_want_write(filp->f_path.mnt);
+		err = mnt_want_write_file(filp);
 		if (err)
 			return err;
 
@@ -206,7 +206,7 @@
 		if (!capable(CAP_SYS_RESOURCE))
 			return -EPERM;
 
-		err = mnt_want_write(filp->f_path.mnt);
+		err = mnt_want_write_file(filp);
 		if (err)
 			return err;
 
@@ -232,7 +232,7 @@
 		if (!capable(CAP_SYS_RESOURCE))
 			return -EPERM;
 
-		err = mnt_want_write(filp->f_path.mnt);
+		err = mnt_want_write_file(filp);
 		if (err)
 			return err;