After ftrace_trace_function is called r1 is probably clobbered so don't
try to use its value for restoring.

This was introduced in v2.6.29~38^2~7
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>