net: xilinx: Fix kernel-doc for axi_mrmac function parameters

net: xilinx: Fix kernel-doc for axi_mrmac function parameters

The kernel-doc comment for the axi_mrmac_recv function was missing
the colon (':') after the '@packetp' parameter tag.

The kernel-doc comment for the axi_mrmac_free_pkt function was missing
the colon (':') after the 'length' parameter tag.

This caused a Sparse warnings regarding the 'packetp' and 'length'
parameters not being described. Fix the formatting to align
with kernel-doc standards and resolve the warning.

drivers/net/xilinx_axi_mrmac.c:357:
warning: Function parameter or member 'packetp' not described
in 'axi_mrmac_recv'
drivers/net/xilinx_axi_mrmac.c:411:
warning: Function parameter or member 'length' not described
in 'axi_mrmac_free_pkt'

Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@amd.com>
Link: https://lore.kernel.org/r/20250717044855.1359443-1-venkatesh.abbarapu@amd.com
Signed-off-by: Michal Simek <michal.simek@amd.com>