[PATCH] amba-pl010: clear error flags on rx error

The pl010 primecell documentation specifies that an error indicated via RSR
should be cleared by a write to ECR.  We didn't do this, which was causing
errors to be re-reported on every call to pl010_rx_chars().

Doing a write to ECR once we detect an error appears to prevent the ep93xx
console UART driver from going into a mode where it reports "ttyAM0: X
input overrun(s)" every couple of keystrokes.

Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>