selftests: drivers/dma-buf: Improve message in selftest summary

Selftest udmabuf for the dma-buf driver is skipped when the device file
(e.g. /dev/udmabuf) for the DMA buffer cannot be opened i.e. no DMA buffer
has been allocated.

This patch adds clarity to the SKIP message.
Signed-off-by: Soumya Negi <soumya.negi97@gmail.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/drivers/dma-buf/udmabuf.c

@@ -32,7 +32,8 @@ int main(int argc, char *argv[])
 
 	devfd = open("/dev/udmabuf", O_RDWR);
 	if (devfd < 0) {
-		printf("%s: [skip,no-udmabuf]\n", TEST_PREFIX);
+		printf("%s: [skip,no-udmabuf: Unable to access DMA buffer device file]\n",
+		       TEST_PREFIX);
 		exit(77);
 	}