Fix up remaining devm_ioremap_nocache() in SGI IOC3 8250 UART driver

This is a merge error on my part - the driver was merged into mainline
by commit c5951e7c ("Merge tag 'mips_5.6' of git://../mips/linux")
over a week ago, but nobody apparently noticed that it didn't actually
build due to still having a reference to the devm_ioremap_nocache()
function, removed a few days earlier through commit 6a1000bd ("Merge
tag 'ioremap-5.6' of git://../ioremap"

).

Apparently this didn't get any build testing anywhere.  Not perhaps all
that surprising: it's restricted to 64-bit MIPS only, and only with the
new SGI_MFD_IOC3 support enabled.

I only noticed because the ioremap conflicts in the ARM SoC driver
update made me check there weren't any others hiding, and I found this
one.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>