staging: sm750fb: Fix bugs introduced by early commits

Early commit 30ca5cb6 ("staging: sm750fb: change definition of
PANEL_PLANE_TL fields") and 27b047bb ("staging: sm750fb: change
definition of PANEL_PLANE_BR fields") modify the register bit fields
definitions. But the modifications are wrong, because the bit mask of
"bit field 10:0" is not 0xeff, but 0x7ff. The wrong definition bugs
makes display very strange.

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Cc: stable <stable@vger.kernel.org> # 4.6+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>