clk: vt8500: don't return possibly uninitialized data

The clk-vt8500.c driver would previously enter an endless loop
when invalid settings got requested, this was now fixed. However,
the driver will now return uninitialized data for a subset of those
cases instead, as the gcc correctly warns:

clk/clk-vt8500.c: In function 'wm8650_find_pll_bits':
clk/clk-vt8500.c:423:12: error: 'best_div2' may be used uninitialized in this function [-Werror=maybe-uninitialized]
  *divisor2 = best_div2;
            ^
clk/clk-vt8500.c:422:12: error: 'best_div1' may be used uninitialized in this function [-Werror=maybe-uninitialized]
  *divisor1 = best_div1;
            ^
clk/clk-vt8500.c:421:14: error: 'best_mul' may be used uninitialized in this function [-Werror=maybe-uninitialized]
  *multiplier = best_mul;

This reworks the error handling in the driver so we now return
-EINVAL from clk_round_rate() and clk_set_rate() when we get
impossible inputs.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 090341b0 ("clk: vt8500: fix sign of possible PLL values")
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>