net: ethernet: qualcomm: remove unneeded 'fast_io' parameter in regmap_config

When using MMIO with regmap, fast_io is implied. No need to set it
again.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Luo Jie <jie.luo@oss.qualcomm.com>
Link: https://patch.msgid.link/20260705164208.2184-2-wsa+renesas@sang-engineering.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>