sb/amd: Remove dead assignment in SPI driver

Value stored to 'cmd' is never read

Change-Id: I794b6e12f5af272705cd996f7ca5099e9b9dbfc7
Found-by: scan-build from clang 6
Signed-off-by: Paul Menzel <pmenzel@molgen.mpg.de>
Reviewed-on: https://review.coreboot.org/29568
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
diff --git a/src/southbridge/amd/agesa/hudson/spi.c b/src/southbridge/amd/agesa/hudson/spi.c
index 74c4711..9484651 100644
--- a/src/southbridge/amd/agesa/hudson/spi.c
+++ b/src/southbridge/amd/agesa/hudson/spi.c
@@ -132,7 +132,7 @@
 	reset_internal_fifo_pointer();
 	/* Skip the bytes we sent. */
 	for (count = 0; count < bytesout; count++) {
-		cmd = spi_read(SPI_REG_FIFO);
+		spi_read(SPI_REG_FIFO);
 	}
 
 	for (count = 0; count < bytesin; count++, din++) {