iopoll: Tweak min sleep time used with usleep_range()

Users of the iopoll macros may need to poll addresses that take
a long time to update. In such cases, the hardcoded value of 1 us
passed as the minimum delay to usleep_range() may result in
reads that occur more often than necessary.

Use (sleep_us/4) as the min delay instead of 1 us to resolve this
is a scalable way.

Change-Id: I8f679a7ecdb9ea2666c78aabca3c8ba806e0ead3
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>
diff --git a/include/linux/iopoll.h b/include/linux/iopoll.h
index 0104abc..7169870 100644
--- a/include/linux/iopoll.h
+++ b/include/linux/iopoll.h
@@ -43,7 +43,7 @@
 		if ((cond) || (timeout_us && time_after(jiffies, timeout))) \
 			break; \
 		if (sleep_us) \
-			usleep_range(1, sleep_us); \
+			usleep_range(DIV_ROUND_UP(sleep_us, 4), sleep_us); \
 	} \
 	(cond) ? 0 : -ETIMEDOUT; \
 })