clk: at91: usb: continue if clk_hw_round_rate() return zero

clk: at91: usb: continue if clk_hw_round_rate() return zero

clk_hw_round_rate() may call round rate function of its parents. In case
of SAM9X60 two of USB parrents are PLLA and UPLL. These clocks are
controlled by clk-sam9x60-pll.c driver. The round rate function for this
driver is sam9x60_pll_round_rate() which call in turn
sam9x60_pll_get_best_div_mul(). In case the requested rate is not in the
proper range (rate < characteristics->output[0].min &&
rate > characteristics->output[0].max) the sam9x60_pll_round_rate() will
return a negative number to its caller (called by
clk_core_round_rate_nolock()). clk_hw_round_rate() will return zero in
case a negative number is returned by clk_core_round_rate_nolock(). With
this, the USB clock will continue its rate computation even caller of
clk_hw_round_rate() returned an error. With this, the USB clock on SAM9X60
may not chose the best parent. I detected this after a suspend/resume
cycle on SAM9X60.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lkml.kernel.org/r/1579261009-4573-2-git-send-email-claudiu.beznea@microchip.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>