video: fbdev: xen: remove setting of 'transp' parameter

cppcheck reports
[drivers/video/fbdev/xen-fbfront.c:226]: (style) Assignment of function parameter has no effect outside the function.

The value parameter 'transp' is not used, so setting it can be removed.

Signed-off-by: Tom Rix <trix@redhat.com>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Helge Deller <deller@gmx.de>