mwl8k: Add missing check after DMA map

The DMA map functions can fail and should be tested for errors.
If the mapping fails, unmap and return an error.

Fixes: 788838eb ("mwl8k: use pci_unmap_addr{,set}() to keep track of unmap addresses on rx")
Signed-off-by: Thomas Fourier <fourier.thomas@gmail.com>
Link: https://patch.msgid.link/20250709111339.25360-2-fourier.thomas@gmail.com


Signed-off-by: Johannes Berg <johannes.berg@intel.com>