compositor: Use weston_log rather than perror for error messages

weston_log() seems to be the standard elsewhere in the codebase for
errors.  These are the only two instances where perror() is used
instead, and their error messages aren't that informative anyway.

Signed-off-by: Bryce Harrington <b.harrington@samsung.com>

src/compositor-wayland.c

@@ -211,13 +211,13 @@ wayland_output_get_shm_buffer(struct wayland_output *output)
 
 	fd = os_create_anonymous_file(height * stride);
 	if (fd < 0) {
-		perror("os_create_anonymous_file");
+		weston_log("could not create an anonymous file buffer: %m\n");
 		return NULL;
 	}
 
 	data = mmap(NULL, height * stride, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
 	if (data == MAP_FAILED) {
-		perror("mmap");
+		weston_log("could not mmap %d memory for data: %m\n", height * stride);
 		close(fd);
 		return NULL;
 	}