staging: sm750fb: Rename maxW to max_w in lynx_cursor

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

This change also fixes the following checkpatch CHECK:

CHECK: Avoid CamelCase: <maxW>
115: FILE: drivers/staging/sm750fb/sm750.c:115:
+	if (fbcursor->image.width > cursor->maxW ||

Signed-off-by: Benjamin Philip <benjamin.philip495@gmail.com>
Link: https://lore.kernel.org/r/c0c84569b155df7b510a505a86863987836e192d.1627304144.git.benjamin.philip495@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>