spi: loopback-test: fix spelling mistake: "missmatch" -> "mismatch"

trivial fix to spelling mistake in dev_err message
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-loopback-test.c

@@ -536,7 +536,7 @@ static int spi_test_check_loopback_result(struct spi_device *spi,
 
 mismatch_error:
 	dev_err(&spi->dev,
-		"loopback strangeness - transfer missmatch on byte %04zx - expected 0x%02x, but got 0x%02x\n",
+		"loopback strangeness - transfer mismatch on byte %04zx - expected 0x%02x, but got 0x%02x\n",
 		i, txb, rxb);
 
 	return -EINVAL;