x86/EISA: Dereference memory directly instead of using readl()

x86/EISA: Dereference memory directly instead of using readl()

Sparse expect an __iomem pointer, but after converting the EISA probe to
memremap() the pointer is a regular memory pointer. Access it directly
instead.

[ tglx: Converted it to fix the already applied version  ]

Fixes: 80a4da05642c ("x86/EISA: Use memremap() to probe for the EISA BIOS signature")
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/alpine.DEB.2.21.2408261015270.30766@angie.orcam.me.uk