cxl/Documentation: Fix typo in sysfs write_bandwidth attribute path

Fix a typo in the sysfs documentation for the CXL "write_bandwidth"
attribute path. The attribute was incorrectly documented as write_banwidth.
Update it to the correct write_bandwidth to align with the actual
implementation.

Signed-off-by: Alok Tiwari <alok.a.tiwari@oracle.com>
Link: https://patch.msgid.link/20250516103855.3820882-1-alok.a.tiwari@oracle.com


Signed-off-by: Dave Jiang <dave.jiang@intel.com>