USB: Remove BKL from lseek implementations

Replace it by
mutex_lock(&file->f_dentry->d_inode->i_mutex);
following the example of the generic method

Signed-off-by: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index 6e73150..300f65f 100644
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -122,7 +122,7 @@
 {
 	loff_t ret;
 
-	lock_kernel();
+	mutex_lock(&file->f_dentry->d_inode->i_mutex);
 
 	switch (orig) {
 	case 0:
@@ -138,7 +138,7 @@
 		ret = -EINVAL;
 	}
 
-	unlock_kernel();
+	mutex_unlock(&file->f_dentry->d_inode->i_mutex);
 	return ret;
 }