spi/pl022: Fix calculate_effective_freq()

spi/pl022: Fix calculate_effective_freq()

calculate_effective_freq() was still not optimized and there were cases when it
returned without error and with values of cpsr and scr as zero.

Also, the variable named found is not used well.

This patch targets to optimize and correct this routine. Tested for SPEAr.

Signed-off-by: Viresh Kumar <[email protected]>
Tested-by: Vinit Kamalaksha Shenoy <[email protected]>
Acked-by: Linus Walleij <[email protected]>
Signed-off-by: Grant Likely <[email protected]>