Add casts to avoid build warnings with gcc-4.7

Example:
keystore.cpp:1339:35: error: narrowing conversion of 'CommandCodes[0]'
from 'command_code_t {aka unsigned char}' to 'int8_t {aka signed char}'

Change-Id: I8cd239880821724050d1716b78851807e0246ef2
Signed-off-by: Pavel Chupin <pavel.v.chupin@intel.com>
diff --git a/keystore/keystore_client.cpp b/keystore/keystore_client.cpp
index db9eb68..a3a51ec 100644
--- a/keystore/keystore_client.cpp
+++ b/keystore/keystore_client.cpp
@@ -47,7 +47,7 @@
             return SYSTEM_ERROR;
         }
 
-        uint8_t bytes[2] = { argLen >> 8, argLen };
+        uint8_t bytes[2] = { (uint8_t)(argLen >> 8), (uint8_t)argLen };
         if (TEMP_FAILURE_RETRY(send(sock, bytes, 2, MSG_NOSIGNAL)) != 2
                 || TEMP_FAILURE_RETRY(send(sock, arg, argLen, MSG_NOSIGNAL))
                         != static_cast<ssize_t>(argLen)) {