tpm: Switch to platform_get_irq_optional()

platform_get_irq() calls dev_err() on an error. As the IRQ usage in the
tpm_tis driver is optional, this is undesirable.

Specifically this leads to this new false-positive error being logged:
[    5.135413] tpm_tis MSFT0101:00: IRQ index 0 not found

This commit switches to platform_get_irq_optional(), which does not log
an error, fixing this.

Fixes: 7723f4c5 ("driver core: platform: Add an error message to platform_get_irq*()"
Cc: <stable@vger.kernel.org> # 5.4.x
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>