genwqe: card_base: Use true and false for boolean values

Return statements in functions returning bool should use true or false
instead of an integer value.

This code was detected with the help of Coccinelle.
Signed-off-by: NGustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/genwqe/card_base.h

@@ -497,7 +497,7 @@ int  genwqe_user_vunmap(struct genwqe_dev *cd, struct dma_mapping *m);
 static inline bool dma_mapping_used(struct dma_mapping *m)
 {
 	if (!m)
-		return 0;
+		return false;
 	return m->size != 0;
 }