The return value of bcm2835_clock_rate_from_divisor is always unsigned
and also all caller expect this. So fix the declaration accordingly.

Fixes: 41691b88 ("clk: bcm2835: Add support for programming the audio domain clocks")
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Link: https://lore.kernel.org/r/20220904141037.38816-1-stefan.wahren@i2se.comReviewed-by: Ivan T. Ivanov <iivanov@suse.de>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>