Change kB to KiB

Change the style of the units to KiB, according to
https://docs.mbed.com/docs/writing-and-publishing-guides/en/latest/units/
diff --git a/yotta/data/example-benchmark/main.cpp b/yotta/data/example-benchmark/main.cpp
index 44e66d9..d13cde5 100644
--- a/yotta/data/example-benchmark/main.cpp
+++ b/yotta/data/example-benchmark/main.cpp
@@ -229,7 +229,7 @@
         CODE;                                                           \
     }                                                                   \
                                                                         \
-    mbedtls_printf( "%9lu kB/s,  %9lu cycles/byte\r\n",                  \
+    mbedtls_printf( "%9lu KiB/s,  %9lu cycles/byte\r\n",                  \
                      i * BUFSIZE / 1024,                                \
                      ( mbedtls_timing_hardclock() - tsc ) / ( j * BUFSIZE ) );         \
 } while( 0 )