drm/i915/dg2: Print PHY name properly on calibration error

We need to use phy_name() to convert the PHY value into a human-readable
character in the error message.

Fixes: a6a12811

 ("drm/i915/dg2: Wait for SNPS PHY calibration during display init")
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Swathi Dhanavanthri <swathi.dhanavanthri@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220215163545.2175730-1-matthew.d.roper@intel.com