staging: sm750fb: Rename oScreen to o_screen in lynxfb_crtc

staging: sm750fb: Rename oScreen to o_screen in lynxfb_crtc

The struct lynxfb_crtc has a member named oScreen. This name is
CamelCase and is frowned upon. This commit renames it to o_screen
and makes the necessary changes for the module to build.

This change also fixes the following checkpatch CHECKs:

CHECK: Avoid CamelCase: <oScreen>
138: FILE: sm750.h:138:
+	int oScreen; /* onscreen address offset in vidmem */

CHECK: Avoid CamelCase: <oScreen>
178: FILE: sm750.c:178:
+	base = par->crtc.oScreen;

Signed-off-by: Benjamin Philip <benjamin.philip495@gmail.com>
Link: https://lore.kernel.org/r/8d7c72027f7bc31a1c35a34f9909fa04f4cf8972.1627413010.git.benjamin.philip495@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>