regression 6018: reduce the number of blocks written

Reduces the number of blocks written when testing RPMB filesystem to
avoid occasional out of memory errors.

Acked-by: Jerome Forissier <jerome.forissier@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/host/xtest/regression_6000.c b/host/xtest/regression_6000.c
index a567e76..ee37c5b 100644
--- a/host/xtest/regression_6000.c
+++ b/host/xtest/regression_6000.c
@@ -1713,7 +1713,7 @@
 
 	if (storage_is(storage_id, TEE_STORAGE_PRIVATE_RPMB)) {
 		/* RPMB FS is a bit resource constrained */
-		num_blocks = 20;
+		num_blocks = 10;
 		block_size = 1024;
 	} else {
 		num_blocks = 40;