ARM: OMAP3: Clean up spurious interrupt check logic

SPURIOUSIRQ is contained in bits 31:7 of INTC_SIR, so
INTC_SIR must be right shifted by 7, not 6.

No change in logic, only changes for better readability.
Refer to register definition of INTCPS_SIR_IRQ in OMAP3 Manual.

Signed-off-by: Roger Quadros <ext-roger.quadros@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>