Revert "HACK: f_fs: allocate DMA capable req buffer"

This hack was originally committed in order to get the legacy USB2.0 UDC
device working without wiring up the IOMMU.  Since we're now using the
XUDC device, which supports 64-bit DMA, this hack is no longer needed.

This reverts commit 5f1219b.

BUG=b:27362803
TEST=Build and boot on Smaug; adb still works.

Change-Id: I72fc38d89b819519dd2a4c9a6f43599431f280f4
Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/329381
Reviewed-by: Benson Leung <bleung@chromium.org>
(cherry picked from commit 5ba5f62ca8abc13432aa4cbd1ddf92e842677309)
Reviewed-on: https://chromium-review.googlesource.com/329361

drivers/usb/gadget/function/f_fs.c

@@ -752,7 +752,7 @@ static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
 			   io_data->len;
 		spin_unlock_irq(&epfile->ffs->eps_lock);
 
-		data = kmalloc(data_len, GFP_DMA);
+		data = kmalloc(data_len, GFP_KERNEL);
 		if (unlikely(!data))
 			return -ENOMEM;
 		if (io_data->aio && !io_data->read) {