arm/plat-mxc: Fix forgotten renaming in timer.c

Commit "mxc: Change gpt timer code to be more generic by using V2
instead of MX3" forgot to replace one occurence causing a build
failure.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Cc: Amit Kucheria <amit.kucheria@canonical.com>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>