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 <zhansayabagdaulet@gmail.com>
Link: https://lore.kernel.org/r/74471865b399584d73a18696d2008006301dfd71.1617708653.git.zhansayabagdaulet@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8712/rtl871x_recv.h

@@ -135,7 +135,7 @@ int recv_func(struct _adapter *padapter, void *pcontext);
 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;
 }
@@ -143,7 +143,7 @@ static inline u8 *get_rxmem(union recv_frame *precvframe)
 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;
 }
@@ -153,7 +153,7 @@ static inline u8 *recvframe_pull(union recv_frame *precvframe, sint sz)
 	/* 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) {
@@ -170,7 +170,7 @@ static inline u8 *recvframe_put(union recv_frame *precvframe, sint sz)
 	 * 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) {
@@ -188,7 +188,7 @@ static inline u8 *recvframe_pull_tail(union recv_frame *precvframe, sint sz)
 	 * 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) {