um: random: Don't initialise hwrng struct with zero

Initialising the hwrng struct with zeros causes a
compile-time sparse warning:

 $ ARCH=um make -j10 W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__'
 ...
 CHECK   arch/um/drivers/random.c
 arch/um/drivers/random.c:31:31: sparse: warning: Using plain integer as NULL pointer

Fix the warning by not initialising the hwrng struct
with zeros as it is initialised anyway during module
init.

Fixes: 72d3e093af ("um: random: Register random as hwrng-core device")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Christopher Obbard <chris.obbard@collabora.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/drivers/random.c

@@ -28,7 +28,7 @@
  * protects against a module being loaded twice at the same time.
  */
 static int random_fd = -1;
-static struct hwrng hwrng = { 0, };
+static struct hwrng hwrng;
 static DECLARE_COMPLETION(have_data);
 
 static int rng_dev_read(struct hwrng *rng, void *buf, size_t max, bool block)