i3c: master: Fix missing 'ret' assignment in set_speed()

i3c: master: Fix missing 'ret' assignment in set_speed()

Fix a probe failure in the i3c master driver that occurs when no i3c
devices are connected to the bus.

The issue arises in `i3c_master_bus_init()` where the `ret` value is not
updated after calling `master->ops->set_speed()`. If no devices are
present, `ret` remains set to `I3C_ERROR_M2`, causing the code to
incorrectly proceed to `err_bus_cleanup`.

Cc: stable@vger.kernel.org
Fixes: aef79e189ba2 ("i3c: master: support to adjust first broadcast address speed")
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Mukesh Kumar Savaliya <quic_msavaliy@quicinc.com>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20250108225533.915334-1-Frank.Li@nxp.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>