ata: avoid gcc-7 warning in ata_timing_quantize

ata: avoid gcc-7 warning in ata_timing_quantize

gcc-7 warns about the result of a constant multiplication used as
a boolean:

drivers/ata/libata-core.c: In function 'ata_timing_quantize':
drivers/ata/libata-core.c:3164:30: warning: '*' in boolean context, suggest '&&' instead [-Wint-in-bool-context]

This slightly rearranges the macro to simplify the code and avoid
the warning at the same time.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Tejun Heo <tj@kernel.org>