net: ibm: emac: Use __iomem annotation for emac_[xg]aht_base

net: ibm: emac: Use __iomem annotation for emac_[xg]aht_base

dev->emacp contains an __iomem pointer and values derived
from it are used as __iomem pointers. So use this annotation
in the return type for helpers that derive pointers from dev->emacp.

Flagged by Sparse as:

.../core.c:444:36: warning: incorrect type in argument 1 (different address spaces)
.../core.c:444:36:    expected unsigned int volatile [noderef] [usertype] __iomem *addr
.../core.c:444:36:    got unsigned int [usertype] *
.../core.c: note: in included file:
.../core.h:416:25: warning: cast removes address space '__iomem' of expression

Compile tested only.
No functional change intended.

Signed-off-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20240906-emac-iomem-v1-1-207cc4f3fed0@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>