staging: sm750fb: Remove typedef from "typedef enum _spolarity_t"

This patch removes typedefs from enum and renames it from "typedef enum
_spolarity_t" to "enum spolarity" as per kernel coding standards."

Signed-off-by: Arushi Singhal <arushisinghal19971997@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>