drm/xe: Fix arg to pci_iomap()

drm/xe: Fix arg to pci_iomap()

Commit 2d8865b27724 ("drm/xe: Move BAR definitions to dedicated file")
moved the BAR definition to the header, but replaced the wrong arg in
the pci_iomap() function - the last arg is actuall the length, not the
BAR. Luckily GTTMMADR_BAR == 0, so it still works. Fix the argument
to avoid confusion.

Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Alan Previn <alan.previn.teres.alexis@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240906032507.2952859-1-lucas.demarchi@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>