clk: pxa: Use __iomem properly and staticize lock variable

This function is passed an __iomem pointer but we use a u32
pointer instead which makes checkers like spare complain.
Furthermore, "lock" is a pretty poor variable name for a string
that will go into lockdep reports and the symbol isn't marked
static. Cleanup all this.

Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>