ata: make lba_{28,48}_ok() use ATA_MAX_SECTORS{,_LBA48}

Since we set ATA_MAX_SECTORS_LBA48 to 65535 to avoid the corner case
in some drives that commands with "count" set to 0000h (which
reprsents 65536) does not work as expected, lba_48_ok(), which is
used for number-of-blocks checking when libata pack commands, should
use the same limit as well. In fact, there is no reason for the two
functions not to use the macros anyway.

Signed-off-by: Tom Yan <tom.ty89@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>