ARM: 7459/1: irda/pxa: use readl_relaxed() to access OSCR register

After c00184f9ab4 "ARM: sa11x0/pxa: convert OS timer registers to IOMEM",
magician_defconfig and a few others fail to build because the OSCR
register is accessed by the drivers/net/irda/pxaficp_ir.c but has turned
into a pointer that needs to be read using readl.

There are other registers in the same driver that eventually should
be converted, and it's unclear whether we would want a better interface
to access the OSCR from a device driver.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>