i3c: mipi-i3c-hci: Remove nonexistent ring interrupt

i3c: mipi-i3c-hci: Remove nonexistent ring interrupt

Ring interrupt bit 7, INTR_WARN_INS_STOP_MODE was probably drafted at
some point but is marked as reserved in the MIPI I3C HCI specification
versions 1.1 and 1.2 that came out after the initial code and also in
the earlier specification versions so remove it.

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/r/20250827103009.243771-3-jarkko.nikula@linux.intel.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>