genirq: Calculate precision only when required

genirq: Calculate precision only when required

Calculating the precision of the interrupt number column on every initial
show_interrupt() invocation is a pointless exercise as the underlying
maximum number of interrupts rarely changes.

Calculate it only when that number is modified and let show_interrupts()
use the cached value.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Dmitry Ilvokhin <d@ilvokhin.com>
Reviewed-by: Radu Rendec <radu@rendec.net>
Link: https://patch.msgid.link/20260517194931.760664517@kernel.org