serial: PL011: move interrupt clearing

Commit 360f748b204275229f8398cb2f9f53955db1503b
"serial: PL011: clear pending interrupts"
attempts to clear interrupts by writing to a
yet-unassigned memory address. This fixes the issue.

The breaking patch is marked for stable so should be
carried along with the other patch.

Cc: Shreshtha Kumar Sahu <shreshthakumar.sahu@stericsson.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: stable <stable@vger.kernel.org>
Cc: Nicolas Pitre <nico@fluxnic.net>
Reported-by: Viresh Kumar <viresh.kumar@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>