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]