As platform_get_irq() now prints an error when the interrupt does not
exist, counting interrupts by looping until failure causes the printing
of scary messages like:

    renesas_sdhi_internal_dmac ee140000.sd: IRQ index 1 not found

Fix this by using the platform_irq_count() helper to avoid touching
non-existent interrupts.

Fixes: 7723f4c5 ("driver core: platform: Add an error message to platform_get_irq*()")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>