i3c: master: adi: fix number of bytes written to fifo

adi_i3c_master_wr_to_tx_fifo computes the maximum number of bytes that can be
sent to the fifo but never makes use of it, actually limit the number of bytes
sent.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202509190505.fKGvEJRa-lkp@intel.com/


Reviewed-by: Jorge Marques <jorge.marques@analog.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/r/20250924195600.122142-1-alexandre.belloni@bootlin.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>