Ensure unique block address for multi threaded test.

The addresses dont have to change each run, just be unique.
Because address seeds repeat themselves each run, rand() will
produce repeating results that should not collide between
different threads.

components/storage/blockdevice/COMPONENT_SPIF/TESTS/block_device/spif/main.cpp

@@ -47,6 +47,11 @@ void basic_erase_program_read_test(SPIFBlockDevice &block_device, bd_size_t bloc
 {
     int err = 0;
     _mutex->lock();
+
+    // Make sure block address per each test is unique
+    static unsigned block_seed = 1;
+    srand(block_seed++);
+
     // Find a random block
     bd_addr_t block = (rand() * block_size) % block_device.size();