x86/mm/pat: drop duplicate variable in cpa_flush()

There is a 'struct cpa_data *data' parameter in cpa_flush() that is
assigned to a local 'struct cpa_data *cpa' variable.

Rename the parameter from 'data' to 'cpa' and drop declaration of the
local 'cpa' variable.

Signed-off-by: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250126074733.1384926-3-rppt@kernel.org