[media] videobuf2: Fix vb2_write prototype

struct v4_file_operations defines the data param as
const char __user *data but on vb2 is defined as
char __user *data.
This patch fixes the warnings produced by this. ie:
drivers/qtec/qtec_xform.c:817:2: warning: initialization from
incompatible pointer type [enabled by default]
drivers/qtec/qtec_xform.c:817:2: warning: (near initialization for
		‘qtec_xform_v4l_fops.write’) [enabled by default]
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/v4l2-core/videobuf2-core.c

@@ -2467,10 +2467,11 @@ size_t vb2_read(struct vb2_queue *q, char __user *data, size_t count,
 }
 EXPORT_SYMBOL_GPL(vb2_read);
 
-size_t vb2_write(struct vb2_queue *q, char __user *data, size_t count,
+size_t vb2_write(struct vb2_queue *q, const char __user *data, size_t count,
 		loff_t *ppos, int nonblocking)
 {
-	return __vb2_perform_fileio(q, data, count, ppos, nonblocking, 0);
+	return __vb2_perform_fileio(q, (char __user *) data, count,
+							ppos, nonblocking, 0);
 }
 EXPORT_SYMBOL_GPL(vb2_write);
 
@@ -2631,7 +2632,7 @@ int vb2_fop_release(struct file *file)
 }
 EXPORT_SYMBOL_GPL(vb2_fop_release);
 
-ssize_t vb2_fop_write(struct file *file, char __user *buf,
+ssize_t vb2_fop_write(struct file *file, const char __user *buf,
 		size_t count, loff_t *ppos)
 {
 	struct video_device *vdev = video_devdata(file);

include/media/videobuf2-core.h

@@ -391,7 +391,7 @@ unsigned long vb2_get_unmapped_area(struct vb2_queue *q,
 unsigned int vb2_poll(struct vb2_queue *q, struct file *file, poll_table *wait);
 size_t vb2_read(struct vb2_queue *q, char __user *data, size_t count,
 		loff_t *ppos, int nonblock);
-size_t vb2_write(struct vb2_queue *q, char __user *data, size_t count,
+size_t vb2_write(struct vb2_queue *q, const char __user *data, size_t count,
 		loff_t *ppos, int nonblock);
 
 /**
@@ -491,7 +491,7 @@ int vb2_ioctl_expbuf(struct file *file, void *priv,
 
 int vb2_fop_mmap(struct file *file, struct vm_area_struct *vma);
 int vb2_fop_release(struct file *file);
-ssize_t vb2_fop_write(struct file *file, char __user *buf,
+ssize_t vb2_fop_write(struct file *file, const char __user *buf,
 		size_t count, loff_t *ppos);
 ssize_t vb2_fop_read(struct file *file, char __user *buf,
 		size_t count, loff_t *ppos);