tst_device: Increase DEV_SIZE_MB to 300 MB

Previous default 256 MB was not enough for mkfs.xfs since v5.19.0-rc1 [1]
which refuses to create filesystems < 300 MB. Although the limitation
can be workarounded by setting three environment variables, it's better
to increase the variable.

[1]: https://lore.kernel.org/all/164738662491.3191861.15611882856331908607.stgit@magnolia/

Reported-by: Martin Doucha <[email protected]>
Reviewed-by: Li Wang <[email protected]>
Reviewed-by: Cyril Hrubis <[email protected]>
Signed-off-by: Petr Vorel <[email protected]>

Author: pevik

lib/tst_device.c

@@ -44,7 +44,7 @@
 #define LOOP_CONTROL_FILE "/dev/loop-control"
 
 #define DEV_FILE "test_dev.img"
-#define DEV_SIZE_MB 256u
+#define DEV_SIZE_MB 300u
 
 static char dev_path[1024];
 static int device_acquired;