avr32: favr-32: clk_round_rate() can return a zero upon error
avr32: favr-32: clk_round_rate() can return a zero upon error

Treat both negative and zero return values from clk_round_rate() as
errors.  This is needed since subsequent patches will convert
clk_round_rate()'s return value to be an unsigned type, rather than a
signed type, since some clock sources can generate rates higher than
(2^31)-1 Hz.

Eventually, when calling clk_round_rate(), only a return value of zero
will be considered a error.  All other values will be considered valid
rates.  The comparison against values less than 0 is kept to preserve
the correct behavior in the meantime.

Signed-off-by: Paul Walmsley <a027184a55211cd23e3f3094f1fdc728df5e0500@pwsan.com>
Cc: Nicolas Ferre <45b517be0e5ec6dc3a39715767c1d18e090d39b4@atmel.com>
Cc: Håvard Skinnemoen <de7418319212d7eab32260a76732c1f83e514852@gmail.com>
Cc: Hans-Christian Egtvedt <11ce19a6fc3bb47abce595a29a6ea4cfed5efa4c@samfundet.no>
Cc: Jean-Christophe PLAGNIOL-VILLARD <9fc55922e47e21cb004bb878f69efa10ab51cf02@jcrosoft.com>
Acked-by: Hans-Christian Egtvedt <11ce19a6fc3bb47abce595a29a6ea4cfed5efa4c@samfundet.no>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs