staging: rtl8712: Rewrite NULL comparisons

Replace NULL comparisons with boolean negation to be more consistent with
the rest of the Linux kernel code base.
Reported by checkpatch.

Signed-off-by: Zhansaya Bagdauletkyzy <[e-mail]>
Link: https://lore.kernel.org/r/74471865b[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/rtl8712/rtl871x_recv.h

···
 static inline u8 *get_rxmem(union recv_frame *precvframe)
 {
 	/* always return rx_head... */
-	if (precvframe == NULL)
+	if (!precvframe)
 		return NULL;
 	return precvframe->u.hdr.rx_head;
 }
···
 static inline u8 *get_recvframe_data(union recv_frame *precvframe)
 {
 	/* always return rx_data */
-	if (precvframe == NULL)
+	if (!precvframe)
 		return NULL;
 	return precvframe->u.hdr.rx_data;
 }
···
 	/* used for extract sz bytes from rx_data, update rx_data and return
 	 * the updated rx_data to the caller
 	 */
-	if (precvframe == NULL)
+	if (!precvframe)
 		return NULL;
 	precvframe->u.hdr.rx_data += sz;
 	if (precvframe->u.hdr.rx_data > precvframe->u.hdr.rx_tail) {
···
 	 * return the updated rx_tail to the caller
 	 * after putting, rx_tail must be still larger than rx_end.
 	 */
-	if (precvframe == NULL)
+	if (!precvframe)
 		return NULL;
 	precvframe->u.hdr.rx_tail += sz;
 	if (precvframe->u.hdr.rx_tail > precvframe->u.hdr.rx_end) {
···
 	 * updated rx_end to the caller
 	 * after pulling, rx_end must be still larger than rx_data.
 	 */
-	if (precvframe == NULL)
+	if (!precvframe)
 		return NULL;
 	precvframe->u.hdr.rx_tail -= sz;
 	if (precvframe->u.hdr.rx_tail < precvframe->u.hdr.rx_data) {