mips: use fallback for random_get_entropy() instead of zero

In the event that random_get_entropy() can't access a cycle counter or
similar, falling back to returning 0 is really not the best we can do.
Instead, at least calling random_get_entropy_fallback() would be
preferable, because that always needs to return _something_, even
falling back to jiffies eventually. It's not as though
random_get_entropy_fallback() is super high precision or guaranteed to
be entropic, but basically anything that's not zero all the time is
better than returning zero all the time.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

arch/mips/include/asm/timex.h

@@ -94,7 +94,7 @@ static inline unsigned long random_get_entropy(void)
 	else if (likely(imp != PRID_IMP_R6000 && imp != PRID_IMP_R6000A))
 		return read_c0_random();
 	else
-		return 0;	/* no usable register */
+		return random_get_entropy_fallback();	/* no usable register */
 }
 #define random_get_entropy random_get_entropy