staging: sm750fb: Rename oCursor to o_cursor in lynxfb_crtc

staging: sm750fb: Rename oCursor to o_cursor in lynxfb_crtc

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

This change also fixes the following checkpatch CHECK:

CHECK: Avoid CamelCase: <oCursor>
137: FILE: sm750.h:137:
+	int oCursor; /* cursor address offset in vidmem */

Signed-off-by: Benjamin Philip <benjamin.philip495@gmail.com>
Link: https://lore.kernel.org/r/aec911b055687892897feb4899644b9463245f1e.1627413010.git.benjamin.philip495@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>