ata: sata_mv: Replace mdelay with usleep_range in mv_reset_channel

After checking all possible call chains to mv_reset_channel here,
my tool finds that mv_reset_channel is never called in atomic context,
namely never in an interrupt handler or holding a spinlock.
Thus mdelay can be replaced with usleep_range to avoid busy wait.

This is found by a static analysis tool named DCNS written by myself.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>