[ARM] pxa: add parameter to clksrc_read() for pxa168/910

This patch modifies parameter of clksrc_read() from 'void' to
'struct clocksource *cs', which fixes compile warning for
incompatible parameter type.

Signed-off-by: Coly Li <coly.li@suse.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Eric Miao <eric.miao@marvell.com>