ARM: udelay: prevent math rounding resulting in short udelays

ARM: udelay: prevent math rounding resulting in short udelays

We perform the microseconds to loops calculation using a number of
multiplies and shift rights.  Each shift right rounds down the
resulting value, which can result in delays shorter than requested.
Ensure that we always round up.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>